feat: add configurable client ID for WebSocket connect frame

Add a clientId option that can be set via:
- VITE_CLIENT_ID env var at build time
- Advanced section in the login screen at runtime
- Stored in localStorage with other credentials

Defaults to 'webchat' for backward compatibility. Users can set it
to 'openclaw-control-ui' to use OpenClaw's dangerouslyDisableDeviceAuth
bypass without post-install patching.

Closes #11

.env.example

@@ -4,3 +4,7 @@ VITE_GATEWAY_WS_URL=ws://localhost:18789
 
 # Optional: UI locale (default: en). Supported: en, fr
 VITE_LOCALE=en
+
+# Optional: client ID sent in the WebSocket connect frame (default: webchat)
+# Set to "openclaw-control-ui" to use OpenClaw's dangerouslyDisableDeviceAuth bypass
+VITE_CLIENT_ID=webchat