fix(ui): unbreak viz.html — OrbitControls importmap, WS URL, toast NPE (#760)

Three independent bugs were stacking to make ui/viz.html unusable from `main`:

1. Three.js r160 removed `examples/js/OrbitControls.js`, so the script-tag
   load 404'd and `new THREE.OrbitControls(...)` threw. Switch to an
   importmap that pulls the ES module build, then re-expose
   `window.THREE` and `THREE.OrbitControls` so the existing component
   modules (scene.js, body-model.js, …) keep working without a wider
   refactor.

2. The WebSocket client was hardcoded to `ws://localhost:8000/ws/pose`,
   but the sensing-server listens on `--ws-port` (8765 default, 3001 in
   the Docker image) at `/ws/sensing`. Reuse the existing
   `buildSensingWsUrl()` helper from `sensing.service.js` so port
   pairings are handled centrally, and add a `?ws=…` query-string
   override for non-standard setups. The websocket-client.js default is
   also updated to derive from `window.location` instead of the dead
   `:8000/ws/pose` literal.

3. `ToastManager.show()` called `this.container.appendChild(...)` even
   when `init()` had never been called, throwing a TypeError that
   killed the rest of page initialization. Auto-init the container
   lazily on first show (patch from issue reporter).

Closes #760.

Co-Authored-By: claude-flow <ruv@ruv.net>

ui/utils/toast.js

@@ -27,6 +27,8 @@ export class ToastManager {
       action = null
     } = options;
 
+    if (!this.container) this.init();
+
     const id = ++this.idCounter;
     const toast = document.createElement('div');
     toast.className = `toast toast-${type}`;