UI: collapse W axis to home-only (drop set-zero / W-origin)

The W axis homing already drives toward the configured limit (home_dir
in aux.json, default '-') and lands at home_position_mm = 0, so
'home' and 'zero' are the same point. Remove the now-redundant 'W
Origin' (move-to-zero) and 'Set W to 0' map-marker buttons; keep just
W-, W+, and a single Home W button. Also drop the unused
aux_move_zero / aux_set_zero JS handlers.

src/js/control-view.js

@@ -771,12 +771,6 @@ module.exports = {
       });
     },
 
-    aux_set_zero: function () {
-      api.put("aux/set-zero", { mm: 0 }).catch(function (err) {
-        console.error("W set-zero failed:", err);
-      });
-    },
-
     aux_jog: function (delta_mm) {
       api.put("aux/jog", { mm: delta_mm }).catch(function (err) {
         console.error("W jog failed:", err);
@@ -792,14 +786,6 @@ module.exports = {
       this.aux_jog(delta_mm);
     },
 
-    // "W Origin" - move W to 0 (absolute). Distinct from aux_set_zero,
-    // which sets the *current* position as the new zero without moving.
-    aux_move_zero: function () {
-      api.put("aux/move", { mm: 0 }).catch(function (err) {
-        console.error("W move-to-zero failed:", err);
-      });
-    },
-
     show_set_position: function (axis) {
       SvelteComponents.showDialog("SetAxisPosition", { axis });
     },