M1-T05: drop location/poo database config from Settings and tests

Remove the dead location_database_url / poo_database_url fields and the
location_sqlite_path / poo_sqlite_path computed properties from Settings;
drop them from the config-page payload and from .env.example. Update the
test hardcodes (test_config, test_public_ip, test_smtp) and reduce the
conftest test_database_urls fixture to the single app DB. The one-time
migration script keeps reading legacy URLs from env/CLI, independent of
Settings.

pytest 95 passed; ruff clean (pre-existing only).

.env.example

@@ -4,8 +4,6 @@ APP_NAME=Home Automation Backend (Python)
 APP_ENV=production
 APP_HOSTNAME=home-automation.example.com
 APP_DATABASE_URL=sqlite:////app/data/app.db
-LOCATION_DATABASE_URL=sqlite:////app/data/locationRecorder.db
-POO_DATABASE_URL=sqlite:////app/data/pooRecorder.db
 AUTH_BOOTSTRAP_USERNAME=admin
 AUTH_BOOTSTRAP_PASSWORD=change-me