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/integration/test_listing_cache.py

@@ -0,0 +1,132 @@
+"""Integration tests for Redis-based listing cache."""
+import pytest
+
+from models.listing import ListingType, QueryParameters
+from services.listing_cache import (
+    begin_cache_population,
+    cache_features_batch,
+    cache_features_batch_staged,
+    delete_staging_key,
+    finalize_cache_population,
+    get_cached_count,
+    get_cached_features,
+    invalidate_cache,
+    make_cache_key,
+)
+
+
+@pytest.fixture(autouse=True)
+def patch_redis(fake_redis, monkeypatch: pytest.MonkeyPatch) -> None:
+    """Route all cache operations through fakeredis."""
+    monkeypatch.setattr("services.listing_cache._get_redis_client", lambda: fake_redis)
+
+
+def _make_qp(**kwargs) -> QueryParameters:
+    return QueryParameters(listing_type=ListingType.RENT, **kwargs)
+
+
+def _sample_features(n: int) -> list[dict]:
+    return [{"type": "Feature", "id": i, "properties": {"price": 1000 + i}} for i in range(n)]
+
+
+# ---------- Basic read/write ----------
+
+
+def test_cache_miss_returns_none() -> None:
+    qp = _make_qp()
+    assert get_cached_count(qp) is None
+
+
+def test_cache_write_then_read() -> None:
+    qp = _make_qp()
+    features = _sample_features(5)
+    cache_features_batch(qp, features)
+
+    count = get_cached_count(qp)
+    assert count == 5
+
+
+def test_batch_retrieval() -> None:
+    qp = _make_qp()
+    cache_features_batch(qp, _sample_features(10))
+
+    batches = list(get_cached_features(qp, batch_size=3))
+    sizes = [len(b) for b in batches]
+    assert sizes == [3, 3, 3, 1]
+
+
+# ---------- Cache key behaviour ----------
+
+
+def test_cache_key_deterministic() -> None:
+    qp1 = _make_qp()
+    qp2 = _make_qp()
+    assert make_cache_key(qp1) == make_cache_key(qp2)
+
+
+def test_cache_key_different_for_different_params() -> None:
+    rent = _make_qp()
+    buy = QueryParameters(listing_type=ListingType.BUY)
+    assert make_cache_key(rent) != make_cache_key(buy)
+
+
+# ---------- Staged population ----------
+
+
+def test_staged_population_begin() -> None:
+    qp = _make_qp()
+    staging_key = begin_cache_population(qp)
+    assert isinstance(staging_key, str)
+    assert "staging" in staging_key
+
+
+def test_staged_write_then_finalize() -> None:
+    qp = _make_qp()
+    staging_key = begin_cache_population(qp)
+    cache_features_batch_staged(staging_key, _sample_features(4))
+    finalize_cache_population(staging_key, qp)
+
+    assert get_cached_count(qp) == 4
+
+
+def test_staging_key_deleted_on_cleanup(fake_redis) -> None:
+    qp = _make_qp()
+    staging_key = begin_cache_population(qp)
+    cache_features_batch_staged(staging_key, _sample_features(2))
+    delete_staging_key(staging_key)
+
+    assert fake_redis.exists(staging_key) == 0
+
+
+# ---------- Invalidation ----------
+
+
+def test_invalidation() -> None:
+    qp = _make_qp()
+    cache_features_batch(qp, _sample_features(5))
+    assert get_cached_count(qp) == 5
+
+    invalidate_cache()
+    assert get_cached_count(qp) is None
+
+
+# ---------- Edge cases ----------
+
+
+def test_empty_features_batch_noop() -> None:
+    qp = _make_qp()
+    cache_features_batch(qp, [])
+    assert get_cached_count(qp) is None
+
+
+def test_multiple_batches_accumulate() -> None:
+    qp = _make_qp()
+    cache_features_batch(qp, _sample_features(3))
+    cache_features_batch(qp, _sample_features(4))
+    assert get_cached_count(qp) == 7
+
+
+def test_get_cached_features_empty() -> None:
+    qp = _make_qp()
+    batches = list(get_cached_features(qp))
+    assert batches == []