Add authentication features for admin access

- Introduce a new `auth` module with login, logout, and user verification endpoints for a single admin user.
- Update backend routes to require admin authentication for sensitive operations, enhancing security.
- Modify frontend components to include an authentication provider and gate, ensuring only authorized users can access the application.
- Implement a login page for admin access, improving user experience and security management.
- Update API request handling to redirect unauthorized users to the login page, ensuring proper access control.

backend/routes/voice_ws.py

@@ -15,6 +15,7 @@ from db.session import SessionLocal
 from fastapi import APIRouter, WebSocket
 from loguru import logger
 from models import AssistantConfig
+from services.auth import require_admin_websocket
 from services.config_resolver import resolve_runtime_config
 from starlette.websockets import WebSocketDisconnect
 
@@ -38,6 +39,8 @@ async def voice_stream(websocket: WebSocket):
     from services.pipecat.pipeline import run_pipeline
     from services.pipecat.transports import build_ws_transport
 
+    if not await require_admin_websocket(websocket):
+        return
     await websocket.accept()
     try:
         cfg = await _resolve_start_config(await websocket.receive_text())