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_videos.py

@@ -0,0 +1,62 @@
+from datetime import datetime, timezone
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.core.auth_dependency import require_session
+from app.db import get_db
+from app.main import app
+from app.models.category import Category
+from app.models.channel import Channel
+from app.models.channel_category import channel_categories
+from app.models.video import Video
+
+
+@pytest.fixture
+def client(db_session):
+    def _get_db_override():
+        yield db_session
+
+    app.dependency_overrides[get_db] = _get_db_override
+    app.dependency_overrides[require_session] = lambda: None
+    with TestClient(app) as test_client:
+        yield test_client
+    del app.dependency_overrides[get_db]
+    del app.dependency_overrides[require_session]
+
+
+def test_get_video_by_youtube_id(client, db_session):
+    channel = Channel(youtube_channel_id="chanA", title="Channel A", subscribed=True)
+    db_session.add(channel)
+    db_session.commit()
+
+    category = Category(name="Linux", slug="linux", sort_order=0)
+    db_session.add(category)
+    db_session.commit()
+    db_session.execute(channel_categories.insert().values(channel_id=channel.id, category_id=category.id))
+    db_session.commit()
+
+    video = Video(
+        youtube_video_id="vid1",
+        channel_id=channel.id,
+        title="Video One",
+        description="desc",
+        published_at=datetime(2026, 9, 10, tzinfo=timezone.utc),
+        duration_seconds=125,
+        youtube_url="https://www.youtube.com/watch?v=vid1",
+    )
+    db_session.add(video)
+    db_session.commit()
+
+    resp = client.get("/api/videos/vid1")
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["youtube_video_id"] == "vid1"
+    assert body["channel"]["id"] == channel.id
+    assert body["categories"] == [{"id": category.id, "name": "Linux"}]
+    assert body["local"]["available"] is False
+
+
+def test_get_video_not_found(client):
+    resp = client.get("/api/videos/missing")
+    assert resp.status_code == 404