Settings: add W axis (auxcnc) panel

Expose the aux.json fields under a new 'W Axis (auxcnc)' section in
Settings: serial port/baud, mechanics (steps/mm, dir sign, soft limits,
max feed), homing (direction, position, fast/slow seek, backoff, max
travel, limit polarity) and the step profile (max/start rate, accel).

The 'enabled' flag stays read-only in the UI; flipping the W axis
on/off is still done via aux.json so a fresh install can't surprise the
user with hardware that isn't there. Live status (offline / unhomed /
homed at <pos> mm) is shown above the form.

Saving PUTs the merged config to /api/aux/config/save, which writes
aux.json and pushes the homing/step config to the ESP.

src/svelte-components/src/components/SettingsView.svelte

@@ -2,6 +2,7 @@
     import configTemplate from "../../../resources/config-template.json";
     import ScreenRotationDialog from "$dialogs/ScreenRotationDialog.svelte";
     import ConfigTemplatedInput from "./ConfigTemplatedInput.svelte";
+    import WAxisSettings from "./WAxisSettings.svelte";
     import SetTimeDialog from "$dialogs/SetTimeDialog.svelte";
     import Button, { Label } from "@smui/button";
 
@@ -94,6 +95,11 @@
             {/each}
         </fieldset>
 
+        <h2>W Axis (auxcnc)</h2>
+        <fieldset>
+            <WAxisSettings />
+        </fieldset>
+
         <h2>Path Accuracy</h2>
         <fieldset>
             <ConfigTemplatedInput key={`settings.max-deviation`} />

src/svelte-components/src/components/WAxisSettings.svelte

@@ -0,0 +1,262 @@
+<script lang="ts">
+    import { onMount } from "svelte";
+    import Button, { Label } from "@smui/button";
+    import * as api from "$lib/api";
+
+    // Mirrors the DEFAULTS in src/py/bbctrl/AuxAxis.py. The "enabled"
+    // flag is read-only here; toggling the W axis on/off is done via
+    // aux.json on disk, so adding/removing the hardware doesn't have a
+    // surprise UI that bricks bring-up.
+    type AuxConfig = {
+        enabled: boolean;
+        port: string;
+        baud: number;
+        steps_per_mm: number;
+        dir_sign: number;
+        min_w: number;
+        max_w: number;
+        max_feed_mm_min: number;
+        home_dir: string;
+        home_position_mm: number;
+        home_fast_sps: number;
+        home_slow_sps: number;
+        home_backoff_steps: number;
+        home_maxtravel_steps: number;
+        step_max_sps: number;
+        step_accel_sps2: number;
+        step_start_sps: number;
+        limit_low: boolean;
+    };
+
+    let cfg: AuxConfig | null = null;
+    let status: { enabled: boolean; present: boolean; homed: boolean; pos_mm: number } | null = null;
+    let busy = false;
+    let saveMessage = "";
+
+    onMount(async () => {
+        await refresh();
+    });
+
+    async function refresh() {
+        try {
+            cfg = await api.GET("aux/config");
+            status = await api.GET("aux/status");
+        } catch (e) {
+            console.error("Failed to load aux config/status:", e);
+        }
+    }
+
+    async function save() {
+        if (!cfg) return;
+        busy = true;
+        saveMessage = "";
+        try {
+            await api.PUT("aux/config/save", cfg);
+            saveMessage = "Saved.";
+            await refresh();
+            setTimeout(() => (saveMessage = ""), 3000);
+        } catch (e) {
+            console.error("Failed to save aux config:", e);
+            saveMessage = "Save failed - see console.";
+        } finally {
+            busy = false;
+        }
+    }
+</script>
+
+<div class="w-axis-settings">
+    {#if !cfg}
+        <p class="tip">Loading W axis configuration...</p>
+    {:else}
+        <div class="status">
+            {#if status}
+                <span>
+                    Status:
+                    {#if !status.enabled}
+                        disabled
+                    {:else if !status.present}
+                        offline
+                    {:else if status.homed}
+                        homed at {status.pos_mm.toFixed(3)} mm
+                    {:else}
+                        connected, unhomed
+                    {/if}
+                </span>
+            {/if}
+        </div>
+
+        <div class="pure-form pure-form-aligned">
+            <fieldset>
+                <div class="pure-control-group" title="Enable the auxcnc W axis. Edit aux.json to toggle.">
+                    <label for="enabled">enabled</label>
+                    <input id="enabled" type="checkbox" checked={cfg.enabled} disabled />
+                    <label for="" class="units">(edit aux.json)</label>
+                </div>
+
+                <div class="pure-control-group" title="Serial port for the auxcnc ESP32.">
+                    <label for="port">serial port</label>
+                    <input id="port" type="text" bind:value={cfg.port} />
+                </div>
+
+                <div class="pure-control-group" title="Serial baud rate.">
+                    <label for="baud">baud</label>
+                    <input id="baud" type="number" bind:value={cfg.baud} min={1200} step={1} />
+                </div>
+            </fieldset>
+
+            <h3>Mechanics</h3>
+            <fieldset>
+                <div class="pure-control-group" title="Logical steps per mm of W travel.">
+                    <label for="steps_per_mm">steps per mm</label>
+                    <input id="steps_per_mm" type="number" bind:value={cfg.steps_per_mm} step="any" />
+                    <label for="" class="units">steps/mm</label>
+                </div>
+
+                <div class="pure-control-group" title="Direction sign: +1 or -1. Flip if W+ moves the wrong way.">
+                    <label for="dir_sign">direction sign</label>
+                    <select id="dir_sign" bind:value={cfg.dir_sign}>
+                        <option value={1}>+1</option>
+                        <option value={-1}>-1</option>
+                    </select>
+                </div>
+
+                <div class="pure-control-group" title="Soft-limit minimum W in mm.">
+                    <label for="min_w">soft min</label>
+                    <input id="min_w" type="number" bind:value={cfg.min_w} step="any" />
+                    <label for="" class="units">mm</label>
+                </div>
+
+                <div class="pure-control-group" title="Soft-limit maximum W in mm.">
+                    <label for="max_w">soft max</label>
+                    <input id="max_w" type="number" bind:value={cfg.max_w} step="any" />
+                    <label for="" class="units">mm</label>
+                </div>
+
+                <div class="pure-control-group" title="Informational max feed; rate caps live on the ESP.">
+                    <label for="max_feed_mm_min">max feed</label>
+                    <input id="max_feed_mm_min" type="number" bind:value={cfg.max_feed_mm_min} step="any" />
+                    <label for="" class="units">mm/min</label>
+                </div>
+            </fieldset>
+
+            <h3>Homing</h3>
+            <fieldset>
+                <div class="pure-control-group" title="Direction the axis moves when looking for the home limit switch.">
+                    <label for="home_dir">home direction</label>
+                    <select id="home_dir" bind:value={cfg.home_dir}>
+                        <option value="-">- (toward W-)</option>
+                        <option value="+">+ (toward W+)</option>
+                    </select>
+                </div>
+
+                <div class="pure-control-group" title="W position assigned when homing completes.">
+                    <label for="home_position_mm">home position</label>
+                    <input id="home_position_mm" type="number" bind:value={cfg.home_position_mm} step="any" />
+                    <label for="" class="units">mm</label>
+                </div>
+
+                <div class="pure-control-group" title="Fast seek rate during homing search.">
+                    <label for="home_fast_sps">fast seek</label>
+                    <input id="home_fast_sps" type="number" bind:value={cfg.home_fast_sps} step={1} min={1} />
+                    <label for="" class="units">steps/s</label>
+                </div>
+
+                <div class="pure-control-group" title="Slow seek rate during homing latch.">
+                    <label for="home_slow_sps">slow seek</label>
+                    <input id="home_slow_sps" type="number" bind:value={cfg.home_slow_sps} step={1} min={1} />
+                    <label for="" class="units">steps/s</label>
+                </div>
+
+                <div class="pure-control-group" title="Backoff after the limit triggers, before the slow seek.">
+                    <label for="home_backoff_steps">backoff</label>
+                    <input id="home_backoff_steps" type="number" bind:value={cfg.home_backoff_steps} step={1} min={0} />
+                    <label for="" class="units">steps</label>
+                </div>
+
+                <div class="pure-control-group" title="Maximum travel before homing aborts as a runaway.">
+                    <label for="home_maxtravel_steps">max travel</label>
+                    <input id="home_maxtravel_steps" type="number" bind:value={cfg.home_maxtravel_steps} step={1} min={1} />
+                    <label for="" class="units">steps</label>
+                </div>
+
+                <div class="pure-control-group" title="Limit switch active-low? Off = active-high.">
+                    <label for="limit_low">limit active low</label>
+                    <input id="limit_low" type="checkbox" bind:checked={cfg.limit_low} />
+                </div>
+            </fieldset>
+
+            <h3>Step Profile</h3>
+            <fieldset>
+                <div class="pure-control-group" title="Maximum step rate during normal moves.">
+                    <label for="step_max_sps">max rate</label>
+                    <input id="step_max_sps" type="number" bind:value={cfg.step_max_sps} step={1} min={1} />
+                    <label for="" class="units">steps/s</label>
+                </div>
+
+                <div class="pure-control-group" title="Acceleration in steps per second squared.">
+                    <label for="step_accel_sps2">acceleration</label>
+                    <input id="step_accel_sps2" type="number" bind:value={cfg.step_accel_sps2} step={1} min={1} />
+                    <label for="" class="units">steps/s²</label>
+                </div>
+
+                <div class="pure-control-group" title="Initial step rate at the start of a move.">
+                    <label for="step_start_sps">start rate</label>
+                    <input id="step_start_sps" type="number" bind:value={cfg.step_start_sps} step={1} min={1} />
+                    <label for="" class="units">steps/s</label>
+                </div>
+            </fieldset>
+
+            <div class="actions">
+                <Button
+                    touch
+                    variant="raised"
+                    on:click={save}
+                    disabled={busy}
+                >
+                    <Label>Save W Axis Settings</Label>
+                </Button>
+                {#if saveMessage}
+                    <span class="save-msg">{saveMessage}</span>
+                {/if}
+            </div>
+
+            <div class="tip">
+                Changes are written to aux.json. Homing rates and the
+                limit polarity are pushed to the ESP immediately; any
+                running motion is unaffected. Re-home the W axis after
+                changing direction, sign, or step settings.
+            </div>
+        </div>
+    {/if}
+</div>
+
+<style lang="scss">
+    .w-axis-settings {
+        .status {
+            margin-bottom: 1em;
+            font-size: 90%;
+            opacity: 0.8;
+        }
+
+        .actions {
+            margin-left: 210px;
+            margin-top: 1em;
+            display: flex;
+            align-items: center;
+            gap: 1em;
+        }
+
+        .save-msg {
+            font-style: italic;
+        }
+
+        .tip {
+            margin-left: 210px;
+            margin-top: 1em;
+            margin-bottom: 15px;
+            font-style: italic;
+            font-size: 90%;
+            line-height: 1.5;
+        }
+    }
+</style>