kiosk: pi-friendly compact mode + chromium 72 fallbacks

- Detect kiosk mode (localhost / ?kiosk=1) and add html.kiosk-mode
- Suppress 3D path-viewer in kiosk mode (Pi 3B too slow)
- Compact 1366x768 layout: 56px header, smaller jog grid, 4-col macros
  2-col status, 540px jog column
- Flex-gap fallbacks for Chromium 72 (header tabs, sys-btn, state-badge,
  ktab, sp-row, etc.) using "> * + *" margin-* rules
- Path-viewer: opaque WebGL canvas, ResizeObserver-gated render loop,
  no first-frame size flash
- Path-viewer renderer cleared properly on component teardown
- W axis row: W- | W+ | Probe XYZ | Probe Z (was W-|HomeW|W+|Probe)
- Running panel only for actual program execution (not jogging)
- Settings sectioned (Display+Units / Probing / G-code+Motion)
- Routed component now keep-alive across tab swaps
- FA4 -> FA6 webfonts

src/pug/templates/program-view.pug

@@ -82,7 +82,7 @@ script#program-view-template(type="text/x-template")
           span STOP
         button.action-btn(@click="open_folder", :disabled="!is_ready",
           title="Upload a new GCode folder.")
-          .fa.fa-folder-arrow-up.ico
+          .fa.fa-folder-plus.ico
           span UPLOAD FOLDER
         form.gcode-folder-input.file-upload
           input#folderInput(type="file", @change="upload_folder",
@@ -126,10 +126,15 @@ script#program-view-template(type="text/x-template")
           .fa.fa-arrow-down-wide-short
           |  {{files_sortby}}
 
-      // Body: gcode listing on the left, 3D viewer on the right
-      .program-body
+      // Body: gcode listing on the left, 3D viewer on the right.
+      // The 3D path-viewer is suppressed when the UI is loaded by
+      // the Pi's onboard kiosk browser — the VideoCore IV cannot
+      // run three.js at a usable frame rate. Off-Pi clients still
+      // see the full split.
+      .program-body(:class="{'no-preview': is_kiosk}")
         gcode-viewer
-        path-viewer(:toolpath="toolpath", :state="state", :config="config")
+        path-viewer(v-if="!is_kiosk", :toolpath="toolpath",
+          :state="state", :config="config")
 
       .progress-bar(v-if="toolpath_progress && toolpath_progress < 1",
         title="Simulating GCode to check for errors, calculate ETA and generate 3D view.")