ui: assorted polish - Vue async fix, OrbitControls passive listeners, path-viewer + motor-view + indicators

- main.js: disable Vue async batching so reactive writes from
  hashchange listeners propagate synchronously (matches Vue 1's older
  default; avoids dropped DRO updates).
- orbit.js: pass {passive:false} to wheel/touch listeners so
  OrbitControls.preventDefault() actually suppresses page panning.
- path-viewer: opaque dark canvas (no flash from page background),
  zero-size guard, ResizeObserver cleanup on destroy.
- motor-view: stop clobbering user edits with controller state.
- estop/indicators/tool-view/path-viewer pug: rename FA4 icons to FA6,
  add viewBox to estop SVG, fix tool-view trailing newline.

src/pug/templates/path-viewer.pug

@@ -3,7 +3,7 @@ script#path-viewer-template(type="text/x-template")
     .path-viewer-toolbar
       .tool-button(title="Toggle path view size.",
         @click="small = !small", :class="{active: !small}")
-        .fa.fa-arrows-alt
+        .fa.fa-up-down-left-right
 
       .tool-button(@click="showTool = !showTool", :class="{active: showTool}",
         title="Show/hide tool.")