Root cause Blocker #2: `import app.workers.tasks.scrape_cadastre` at module
top-level REBOUND `app` from FastAPI instance (line 14) to the Python package.
All subsequent `app.dependency_overrides[get_db] = ...` failed with
AttributeError because `app` was now the namespace module.
Fix: probe module availability with importlib.util.find_spec — does not
import or rebind names. FastAPI `app` instance stays intact.
All 28 cadastre tests pass locally.