fix: WebSocket wss:// same-origin URL + try/catch to prevent crash on HTTPS

- Change DEFAULT_WS_URL from ws://hostname:3001 to wss://window.location.host
- Wrap WebSocket constructor in try/catch to prevent React crash on connection error
- Fixes white page when opening a project (CADEditor crashed on insecure ws:// from HTTPS page)

frontend/src/crdt/WebSocketProvider.ts

@@ -45,7 +45,14 @@ export class WebSocketProvider {
     this.setStatus('connecting');
 
     const fullUrl = `${this.url}/ws/collab/${encodeURIComponent(this.docName)}`;
-    this.ws = new WebSocket(fullUrl);
+    try {
+      this.ws = new WebSocket(fullUrl);
+    } catch (err) {
+      console.warn('[WebSocketProvider] Failed to construct WebSocket:', err);
+      this.setStatus('error');
+      this.scheduleReconnect();
+      return;
+    }
     this.ws.binaryType = 'arraybuffer';
 
     this.ws.onopen = () => {