Refactor codebase following Clean Code principles and add 229 tests

- Extract helpers to reduce function sizes (listing_tasks, app.py, query.py, listing_fetcher)
  - Replace nonlocal mutations with _PipelineState dataclass in listing_tasks
  - Fix bugs: isinstance→equality check in repository, verify_exp for OIDC tokens
  - Consolidate duplicate filter methods in listing_repository
  - Move hardcoded config to env vars with backward-compatible defaults
  - Simplify CLI decorator to auto-build QueryParameters
  - Add deprecation docstring to data_access.py
  - Test count: 158 → 387 (all passing)

crawler/tests/unit/test_route_serializer.py

@@ -0,0 +1,72 @@
+"""Unit tests for rec/route_serializer.py."""
+from models.listing import DestinationMode, Route, RouteLegStep
+from rec.route_serializer import RouteSerializer
+from rec.routing import TravelMode
+
+
+def _make_sample_routing_info() -> dict[DestinationMode, list[Route]]:
+    destination_mode = DestinationMode(
+        destination_address="London Bridge",
+        travel_mode=TravelMode.TRANSIT,
+    )
+    routes = [
+        Route(
+            legs=[
+                RouteLegStep(
+                    distance_meters=500,
+                    duration_s=120,
+                    travel_mode=TravelMode.WALK,
+                ),
+                RouteLegStep(
+                    distance_meters=4000,
+                    duration_s=480,
+                    travel_mode=TravelMode.TRANSIT,
+                ),
+            ],
+            distance_meters=4500,
+            duration_s=600,
+        )
+    ]
+    return {destination_mode: routes}
+
+
+class TestRouteSerializer:
+    def test_serialize_then_deserialize_roundtrip(self) -> None:
+        routing_info = _make_sample_routing_info()
+        serialized = RouteSerializer.serialize(routing_info)
+        deserialized = RouteSerializer.deserialize(serialized)
+
+        assert len(deserialized) == 1
+        dest_mode = list(deserialized.keys())[0]
+        assert dest_mode.destination_address == "London Bridge"
+        assert dest_mode.travel_mode == TravelMode.TRANSIT
+
+        routes = deserialized[dest_mode]
+        assert len(routes) == 1
+        assert routes[0].distance_meters == 4500
+        assert routes[0].duration_s == 600
+        assert len(routes[0].legs) == 2
+        assert routes[0].legs[0].distance_meters == 500
+        assert routes[0].legs[0].travel_mode == TravelMode.WALK
+        assert routes[0].legs[1].travel_mode == TravelMode.TRANSIT
+
+    def test_deserialize_sample_json(self) -> None:
+        import json
+        import dataclasses
+
+        routing_info = _make_sample_routing_info()
+        # Build the JSON manually to test deserialize independently
+        json_str = json.dumps(
+            {
+                json.dumps(dataclasses.asdict(dm)): [
+                    json.dumps(dataclasses.asdict(r)) for r in routes
+                ]
+                for dm, routes in routing_info.items()
+            }
+        )
+
+        result = RouteSerializer.deserialize(json_str)
+        assert len(result) == 1
+        dest_mode = list(result.keys())[0]
+        assert dest_mode.destination_address == "London Bridge"
+        assert result[dest_mode][0].duration_s == 600