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/config/api.config.js

@@ -1,11 +1,17 @@
 // API Configuration for WiFi-DensePose UI
 
+// Auto-detect the backend URL from the page origin so the UI works whether
+// served from Docker (:3000), local dev (:8080), or any other port.
+const _origin = (typeof window !== 'undefined' && window.location && window.location.origin)
+  ? window.location.origin
+  : 'http://localhost:3000';
+
 export const API_CONFIG = {
-  BASE_URL: 'http://localhost:8080',  // Rust sensing server port
+  BASE_URL: _origin,
   API_VERSION: '/api/v1',
   WS_PREFIX: 'ws://',
   WSS_PREFIX: 'wss://',
-  
+
   // Mock server configuration (only for testing)
   MOCK_SERVER: {
     ENABLED: false,  // Set to true only for testing without backend
@@ -114,9 +120,9 @@ export function buildWsUrl(endpoint, params = {}) {
   const protocol = (isSecure || !isLocalhost)
     ? API_CONFIG.WSS_PREFIX
     : API_CONFIG.WS_PREFIX;
-  
-  // Match Rust sensing server port
-  const host = 'localhost:8080';
+
+  // Derive host from the page origin so it works on any port (Docker :3000, dev :8080, etc.)
+  const host = window.location.host;
   let url = `${protocol}${host}${endpoint}`;
   
   // Add query parameters

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