fix: resolve all 64 mypy errors across backend

- Add dict[str, Any] / list[Any] type params throughout (fingerprint, models, schemas, scanner, status_checker)
- Add return type annotations to all route functions (nodes, edges, canvas, scan, auth, status, main)
- Fix no-any-return in security.py: cast pwd/jwt results to bool/str explicitly
- Fix canvas.py: use model_validate() for NodeResponse/EdgeResponse, rename db_node/db_edge upsert vars
- Fix scheduler.py: rename 'result' → 'check_result' to avoid type collision
- Fix get_db() return type: AsyncGenerator[AsyncSession, None]
- Add types-PyYAML for yaml import stubs
- Fix scanner.py: remove unnecessary type: ignore comment (nmap has stubs)
- Fix scan.py: wrap scalars().all() with list() for Sequence→list compatibility

backend/app/api/routes/status.py

@@ -9,7 +9,7 @@ _connections: list[WebSocket] = []
 
 
 @router.websocket("/ws/status")
-async def ws_status(websocket: WebSocket):
+async def ws_status(websocket: WebSocket) -> None:
     await websocket.accept()
     _connections.append(websocket)
     try:
@@ -19,7 +19,7 @@ async def ws_status(websocket: WebSocket):
         _connections.remove(websocket)
 
 
-async def broadcast_status(node_id: str, status: str, checked_at: str, response_time_ms: int | None = None):
+async def broadcast_status(node_id: str, status: str, checked_at: str, response_time_ms: int | None = None) -> None:
     payload = json.dumps({
         "node_id": node_id,
         "status": status,