Implement Phases 1-5: skeleton, OAuth, categories, video sync/feed, playback

- FastAPI + PostgreSQL + Alembic + React/Vite skeleton, Docker Compose, healthcheck
- Google OAuth (single allowed account), encrypted refresh token storage
- Subscriptions sync with pagination, uploads playlist batch fetch
- Categories CRUD, many-to-many channel assignment, category filtering
- Video sync (playlistItems + videos.list batching), cached feed with cursor
  pagination, background scheduler (APScheduler)
- Video detail page with YouTube embed player
- SPA fallback routing, optimistic UI updates, client-side query caching

40 backend tests covering OAuth allow-list, sync idempotency, cascade deletes,
cursor pagination, and category filtering.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_health.py

@@ -0,0 +1,43 @@
+from unittest.mock import MagicMock, patch
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.db import get_db
+from app.main import app
+
+
+def _fake_db():
+    session = MagicMock()
+    session.execute.return_value = None
+    yield session
+
+
+@pytest.fixture(autouse=True)
+def override_get_db():
+    app.dependency_overrides[get_db] = _fake_db
+    yield
+    del app.dependency_overrides[get_db]
+
+
+def test_health_ok():
+    with patch("app.api.health.httpx.get") as mock_get:
+        mock_get.return_value = MagicMock(status_code=200)
+        client = TestClient(app)
+        response = client.get("/api/health")
+
+    assert response.status_code == 200
+    body = response.json()
+    assert body["status"] == "ok"
+    assert body["database"] == "ok"
+    assert body["metube"] == "ok"
+
+
+def test_health_metube_unreachable():
+    with patch("app.api.health.httpx.get", side_effect=ConnectionError):
+        client = TestClient(app)
+        response = client.get("/api/health")
+
+    assert response.status_code == 200
+    body = response.json()
+    assert body["metube"] == "error"