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).

tests/conftest.py

@@ -20,15 +20,9 @@ def _make_app_alembic_config(database_url: str) -> Config:
 @pytest.fixture
 def test_database_urls(tmp_path: Path, monkeypatch: pytest.MonkeyPatch):
     app_database_path = tmp_path / "app_test.db"
-    location_database_path = tmp_path / "location_test.db"
-    poo_database_path = tmp_path / "poo_placeholder.db"
     app_database_url = f"sqlite:///{app_database_path}"
-    location_database_url = f"sqlite:///{location_database_path}"
-    poo_database_url = f"sqlite:///{poo_database_path}"
 
     monkeypatch.setenv("APP_DATABASE_URL", app_database_url)
-    monkeypatch.setenv("LOCATION_DATABASE_URL", location_database_url)
-    monkeypatch.setenv("POO_DATABASE_URL", poo_database_url)
     monkeypatch.setenv("AUTH_BOOTSTRAP_USERNAME", "admin")
     monkeypatch.setenv("AUTH_BOOTSTRAP_PASSWORD", "test-password")
     monkeypatch.setenv("AUTH_COOKIE_SECURE_OVERRIDE", "false")
@@ -39,10 +33,6 @@ def test_database_urls(tmp_path: Path, monkeypatch: pytest.MonkeyPatch):
         yield {
             "app_path": app_database_path,
             "app_url": app_database_url,
-            "location_path": location_database_path,
-            "location_url": location_database_url,
-            "poo_path": poo_database_path,
-            "poo_url": poo_database_url,
         }
     finally:
         get_settings.cache_clear()