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/requirements.txt

@@ -13,6 +13,7 @@ python-multipart==0.0.22
 apscheduler==3.10.4
 python-nmap==0.7.1
 pyyaml==6.0.2
+types-PyYAML==6.0.12.20240917
 websockets==13.1
 httpx==0.27.2