fix: UI auto-detects server port from page origin (#55)

The UI had hardcoded localhost:8080 for HTTP and localhost:8765 for
WebSocket, causing "Backend unavailable" when served from Docker
(port 3000) or any non-default port.

Changes:
- api.config.js: BASE_URL now uses window.location.origin instead
  of hardcoded localhost:8080
- api.config.js: buildWsUrl() uses window.location.host instead of
  hardcoded localhost:8080
- sensing.service.js: WebSocket URL derived from page origin instead
  of hardcoded localhost:8765
- main.rs: Added /ws/sensing route to the HTTP server so WebSocket
  and REST are reachable on a single port

Fixes #55

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

ui/services/sensing.service.js

@@ -8,7 +8,11 @@
  * always shows something.
  */
 
-const SENSING_WS_URL = 'ws://localhost:8765/ws/sensing';
+// Derive WebSocket URL from the page origin so it works on any port
+// (Docker :3000, native :8080, etc.)
+const _wsProto = (typeof window !== 'undefined' && window.location.protocol === 'https:') ? 'wss:' : 'ws:';
+const _wsHost  = (typeof window !== 'undefined' && window.location.host) ? window.location.host : 'localhost:3000';
+const SENSING_WS_URL = `${_wsProto}//${_wsHost}/ws/sensing`;
 const RECONNECT_DELAYS = [1000, 2000, 4000, 8000, 16000];
 const MAX_RECONNECT_ATTEMPTS = 10;
 const SIMULATION_INTERVAL = 500; // ms