fix: all lint errors, test + lint pre-commit passing

Frontend:
- Split nodeTypes/edgeTypes into separate .ts files (react-refresh)
- Remove setState-in-effect in NodeModal (key prop reset)
- Fix handleSave accessed before declaration (useRef pattern)
- Exclude src/components/ui/** from eslint (shadcn generated)
- Use defineConfig from vitest/config for test type support

Backend:
- ruff --fix: sort imports, datetime.UTC alias
- Raise line-length to 120, ignore E501 in tests
- Break long update_node/update_edge signatures
- pyproject.toml: per-file-ignores for tests

backend/app/api/routes/canvas.py

@@ -1,4 +1,4 @@
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 from fastapi import APIRouter, Depends
 from sqlalchemy import select
@@ -34,7 +34,7 @@ async def save_canvas(body: CanvasSaveRequest, db: AsyncSession = Depends(get_db
     state = await db.get(CanvasState, 1)
     if state:
         state.viewport = body.viewport
-        state.saved_at = datetime.now(timezone.utc)
+        state.saved_at = datetime.now(UTC)
     else:
         db.add(CanvasState(id=1, viewport=body.viewport))