Add comprehensive test suite: 219 new tests across backend and frontend

Backend (103 tests):
- Unit tests for listing_service, export_service, district_service
- Regression tests for API response contracts and query parameter validation
- Integration tests for API workflows, Redis listing cache, listing processor pipeline, and repository advanced queries
- E2E tests for streaming with filters, batching, caching, and task management

Frontend (116 tests):
- Service tests for apiClient, streamingService, taskService, listingService, healthService
- Hook tests for useTaskProgress (WebSocket + polling)
- Component tests for PropertyCard, FilterPanel, Header, ListView, TaskProgressDrawer, TaskIndicator, StreamingProgressBar, HealthIndicator
- E2E tests for filter-stream-display flow

Infrastructure:
- Add pytest-xdist and test markers (regression, integration, e2e)
- Add conftest fixtures: fake_redis, rent_listing_factory, seeded_repository
- Add vitest + testing-library + MSW for frontend testing

tests/unit/test_export_service.py

@@ -0,0 +1,87 @@
+"""Unit tests for services/export_service.py."""
+
+import pytest
+from pathlib import Path
+from unittest.mock import AsyncMock, patch
+
+from models.listing import QueryParameters, ListingType
+from services import export_service
+
+
+class TestExportToCsv:
+    async def test_csv_export_calls_exporter(self, listing_repository, tmp_path):
+        output_path = tmp_path / "output.csv"
+        with patch("csv_exporter.export_to_csv", new_callable=AsyncMock) as mock_csv:
+            mock_csv.return_value = None
+            result = await export_service.export_to_csv(listing_repository, output_path)
+        mock_csv.assert_called_once()
+        assert result.success
+
+    async def test_csv_export_returns_correct_record_count(self, listing_repository, sample_rent_listings, tmp_path):
+        await listing_repository.upsert_listings(sample_rent_listings)
+        output_path = tmp_path / "output.csv"
+        with patch("csv_exporter.export_to_csv", new_callable=AsyncMock) as mock_csv:
+            mock_csv.return_value = None
+            result = await export_service.export_to_csv(listing_repository, output_path)
+        assert result.record_count == len(sample_rent_listings)
+
+    async def test_csv_export_passes_query_parameters(self, listing_repository, tmp_path):
+        output_path = tmp_path / "output.csv"
+        params = QueryParameters(listing_type=ListingType.RENT, min_bedrooms=2)
+        with patch("csv_exporter.export_to_csv", new_callable=AsyncMock) as mock_csv:
+            mock_csv.return_value = None
+            result = await export_service.export_to_csv(
+                listing_repository, output_path, query_parameters=params
+            )
+        assert result.success
+        assert str(output_path) in result.output_path
+
+
+class TestExportToGeojson:
+    async def test_geojson_in_memory_returns_data(self, listing_repository):
+        fake_geojson = {"type": "FeatureCollection", "features": [{"type": "Feature"}]}
+        with patch("ui_exporter.export_immoweb", new_callable=AsyncMock) as mock_export:
+            mock_export.return_value = fake_geojson
+            result = await export_service.export_to_geojson(listing_repository)
+        assert result.data is not None
+        assert result.data["type"] == "FeatureCollection"
+
+    async def test_geojson_file_export_returns_path(self, listing_repository, tmp_path):
+        output_path = tmp_path / "output.geojson"
+        fake_geojson = {"type": "FeatureCollection", "features": []}
+        with patch("ui_exporter.export_immoweb", new_callable=AsyncMock) as mock_export:
+            mock_export.return_value = fake_geojson
+            result = await export_service.export_to_geojson(
+                listing_repository, output_path=output_path
+            )
+        assert result.output_path is not None
+        assert result.data is None
+
+    async def test_geojson_with_filters(self, listing_repository):
+        params = QueryParameters(listing_type=ListingType.RENT, min_bedrooms=2)
+        fake_geojson = {"type": "FeatureCollection", "features": []}
+        with patch("ui_exporter.export_immoweb", new_callable=AsyncMock) as mock_export:
+            mock_export.return_value = fake_geojson
+            result = await export_service.export_to_geojson(
+                listing_repository, query_parameters=params
+            )
+        assert result.success
+        mock_export.assert_called_once()
+
+    async def test_geojson_with_limit(self, listing_repository):
+        fake_geojson = {"type": "FeatureCollection", "features": []}
+        with patch("ui_exporter.export_immoweb", new_callable=AsyncMock) as mock_export:
+            mock_export.return_value = fake_geojson
+            result = await export_service.export_to_geojson(
+                listing_repository, limit=5
+            )
+        assert result.success
+        _, kwargs = mock_export.call_args
+        assert kwargs.get("limit") == 5
+
+    async def test_geojson_empty_data(self, listing_repository):
+        fake_geojson = {"type": "FeatureCollection", "features": []}
+        with patch("ui_exporter.export_immoweb", new_callable=AsyncMock) as mock_export:
+            mock_export.return_value = fake_geojson
+            result = await export_service.export_to_geojson(listing_repository)
+        assert result.record_count == 0