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/services/status_checker.py

@@ -3,13 +3,14 @@ import asyncio
 import logging
 import socket
 import time
+from typing import Any
 
 import httpx
 
 logger = logging.getLogger(__name__)
 
 
-async def check_node(check_method: str, target: str | None, ip: str | None) -> dict:
+async def check_node(check_method: str, target: str | None, ip: str | None) -> dict[str, Any]:
     """
     Run the appropriate check and return {status, response_time_ms}.
     status is one of: online, offline, unknown.