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/main.py

@@ -1,4 +1,6 @@
+from collections.abc import AsyncGenerator
 from contextlib import asynccontextmanager
+from typing import Any
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
@@ -10,7 +12,7 @@ from app.db.database import init_db
 
 
 @asynccontextmanager
-async def lifespan(app: FastAPI):
+async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
     await init_db()
     start_scheduler()
     yield
@@ -40,5 +42,5 @@ app.include_router(status.router, prefix="/api/v1/status", tags=["status"])
 
 
 @app.get("/api/v1/health")
-async def health():
+async def health() -> dict[str, Any]:
     return {"status": "ok"}