Add clickable facet pills for mobile-friendly DSL filter composition

- Create reusable dsl_facets.py component with clickable pills that compose
  DSL filter expressions by appending field:value to the filter input
- Add /api/facets endpoint for dynamic facet count refresh via HTMX
- Fix select dropdown dark mode styling with color-scheme: dark in SelectStyles
- Integrate facet pills into all DSL filter screens: registry, move, and
  all action forms (tag-add, tag-end, attrs, outcome, status-correct)
- Update routes to fetch and pass facet counts, locations, and species
- Add comprehensive unit tests for component and API endpoint
- Add E2E tests for facet pill click behavior and dark mode select visibility

This enables tap-based filter composition on mobile without requiring typing.
Facet counts update dynamically as filters are applied via HTMX.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/test_api_facets.py

@@ -0,0 +1,195 @@
+# ABOUTME: Unit tests for /api/facets endpoint.
+# ABOUTME: Tests dynamic facet count retrieval based on filter.
+
+import os
+import time
+
+import pytest
+from starlette.testclient import TestClient
+
+from animaltrack.events.payloads import AnimalCohortCreatedPayload
+from animaltrack.events.store import EventStore
+from animaltrack.projections import ProjectionRegistry
+from animaltrack.projections.animal_registry import AnimalRegistryProjection
+from animaltrack.projections.event_animals import EventAnimalsProjection
+from animaltrack.projections.intervals import IntervalProjection
+from animaltrack.services.animal import AnimalService
+
+
+def make_test_settings(
+    csrf_secret: str = "test-secret",
+    trusted_proxy_ips: str = "127.0.0.1",
+    dev_mode: bool = True,
+):
+    """Create Settings for testing by setting env vars temporarily."""
+    from animaltrack.config import Settings
+
+    old_env = os.environ.copy()
+    try:
+        os.environ["CSRF_SECRET"] = csrf_secret
+        os.environ["TRUSTED_PROXY_IPS"] = trusted_proxy_ips
+        os.environ["DEV_MODE"] = str(dev_mode).lower()
+        return Settings()
+    finally:
+        os.environ.clear()
+        os.environ.update(old_env)
+
+
+@pytest.fixture
+def client(seeded_db):
+    """Create a test client for the app."""
+    from animaltrack.web.app import create_app
+
+    settings = make_test_settings(trusted_proxy_ips="testclient")
+    app, rt = create_app(settings=settings, db=seeded_db)
+    return TestClient(app, raise_server_exceptions=True)
+
+
+@pytest.fixture
+def projection_registry(seeded_db):
+    """Create a ProjectionRegistry with animal projections registered."""
+    registry = ProjectionRegistry()
+    registry.register(AnimalRegistryProjection(seeded_db))
+    registry.register(EventAnimalsProjection(seeded_db))
+    registry.register(IntervalProjection(seeded_db))
+    return registry
+
+
+@pytest.fixture
+def animal_service(seeded_db, projection_registry):
+    """Create an AnimalService for testing."""
+    event_store = EventStore(seeded_db)
+    return AnimalService(seeded_db, event_store, projection_registry)
+
+
+@pytest.fixture
+def location_strip1_id(seeded_db):
+    """Get Strip 1 location ID from seeded data."""
+    row = seeded_db.execute("SELECT id FROM locations WHERE name = 'Strip 1'").fetchone()
+    return row[0]
+
+
+@pytest.fixture
+def location_strip2_id(seeded_db):
+    """Get Strip 2 location ID from seeded data."""
+    row = seeded_db.execute("SELECT id FROM locations WHERE name = 'Strip 2'").fetchone()
+    return row[0]
+
+
+@pytest.fixture
+def ducks_at_strip1(seeded_db, animal_service, location_strip1_id):
+    """Create 5 female ducks at Strip 1."""
+    payload = AnimalCohortCreatedPayload(
+        species="duck",
+        count=5,
+        life_stage="adult",
+        sex="female",
+        location_id=location_strip1_id,
+        origin="purchased",
+    )
+    ts_utc = int(time.time() * 1000)
+    event = animal_service.create_cohort(payload, ts_utc, "test_user")
+    return event.entity_refs["animal_ids"]
+
+
+@pytest.fixture
+def geese_at_strip2(seeded_db, animal_service, location_strip2_id):
+    """Create 3 male geese at Strip 2."""
+    payload = AnimalCohortCreatedPayload(
+        species="goose",
+        count=3,
+        life_stage="adult",
+        sex="male",
+        location_id=location_strip2_id,
+        origin="purchased",
+    )
+    ts_utc = int(time.time() * 1000)
+    event = animal_service.create_cohort(payload, ts_utc, "test_user")
+    return event.entity_refs["animal_ids"]
+
+
+class TestApiFacetsEndpoint:
+    """Test GET /api/facets endpoint."""
+
+    def test_facets_endpoint_exists(self, client, ducks_at_strip1):
+        """Verify the facets endpoint responds."""
+        response = client.get("/api/facets")
+        assert response.status_code == 200
+
+    def test_facets_returns_html_partial(self, client, ducks_at_strip1):
+        """Facets endpoint returns HTML partial for HTMX swap."""
+        response = client.get("/api/facets")
+        assert response.status_code == 200
+        content = response.text
+
+        # Should be HTML with facet pills structure
+        assert 'id="dsl-facet-pills"' in content
+        assert "Species" in content
+
+    def test_facets_respects_filter(self, client, ducks_at_strip1, geese_at_strip2):
+        """Facets endpoint applies filter and shows filtered counts."""
+        # Get facets filtered to ducks only
+        response = client.get("/api/facets?filter=species:duck")
+        assert response.status_code == 200
+        content = response.text
+
+        # Should show sex facets for ducks (5 female)
+        assert "female" in content.lower()
+        # Should not show goose sex (male) since we filtered to ducks
+        # (actually it might show male=0 or not at all)
+
+    def test_facets_shows_count_for_alive_animals(self, client, ducks_at_strip1):
+        """Facets show counts for alive animals by default."""
+        response = client.get("/api/facets")
+        assert response.status_code == 200
+        content = response.text
+
+        # Should show species with counts
+        assert "duck" in content.lower() or "Duck" in content
+        # Count 5 should appear
+        assert "5" in content
+
+    def test_facets_with_empty_filter(self, client, ducks_at_strip1, geese_at_strip2):
+        """Empty filter returns all alive animals' facets."""
+        response = client.get("/api/facets?filter=")
+        assert response.status_code == 200
+        content = response.text
+
+        # Should have facet pills
+        assert 'id="dsl-facet-pills"' in content
+
+    def test_facets_with_location_filter(self, client, ducks_at_strip1, geese_at_strip2):
+        """Location filter shows facets for that location only."""
+        response = client.get('/api/facets?filter=location:"Strip 1"')
+        assert response.status_code == 200
+        content = response.text
+
+        # Should show ducks (at Strip 1)
+        assert "duck" in content.lower() or "Duck" in content
+
+    def test_facets_includes_htmx_swap_attributes(self, client, ducks_at_strip1):
+        """Returned HTML has proper ID for HTMX swap targeting."""
+        response = client.get("/api/facets")
+        assert response.status_code == 200
+        content = response.text
+
+        # Must have same ID for outerHTML swap to work
+        assert 'id="dsl-facet-pills"' in content
+
+
+class TestApiFacetsWithSelectionPreview:
+    """Test facets endpoint integrates with selection preview workflow."""
+
+    def test_facets_and_preview_use_same_filter(self, client, ducks_at_strip1, geese_at_strip2):
+        """Both endpoints interpret the same filter consistently."""
+        filter_str = "species:duck"
+
+        # Get facets
+        facets_resp = client.get(f"/api/facets?filter={filter_str}")
+        assert facets_resp.status_code == 200
+
+        # Get selection preview
+        preview_resp = client.get(f"/api/selection-preview?filter={filter_str}")
+        assert preview_resp.status_code == 200
+
+        # Both should work with the same filter