Add pytest suite for sample locations with recorded fixtures

Tests replay pre-recorded WDQS and Wikidata API responses so they run
offline against only the local PostGIS database. capture_fixtures.py
records live responses into tests/fixtures/ for later replay.

tests/conftest.py

@@ -0,0 +1,17 @@
+"""Shared pytest fixtures."""
+
+import pytest
+
+
+@pytest.fixture(scope="session")
+def flask_app():
+    """Return the Flask application."""
+    from lookup import app
+    return app
+
+
+@pytest.fixture(scope="session")
+def app_ctx(flask_app):
+    """Push a Flask application context for the whole test session."""
+    with flask_app.app_context():
+        yield