fix: upgrade fastapi to 0.135.1, fix starlette CVEs, update auth test assertions

- fastapi 0.115.0 → 0.135.1 pulls starlette 0.52.1 (fixes CVE-2024-47874, CVE-2025-54121)
- pip-audit: ignore CVE-2024-23342 (ecdsa Minerva attack, no fix exists; app uses HS256 only)
- Update auth guard tests: FastAPI 0.135 returns 401 (not 403) when Bearer token is missing

backend/tests/test_scan.py

@@ -38,8 +38,7 @@ async def pending_device(db_session):
 @pytest.mark.asyncio
 async def test_trigger_scan_requires_auth(client: AsyncClient):
     res = await client.post("/api/v1/scan/trigger")
-    # FastAPI's OAuth2PasswordBearer returns 403 when no token is provided
-    assert res.status_code in (401, 403)
+    assert res.status_code == 401
 
 
 @pytest.mark.asyncio