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/conftest.py

@@ -0,0 +1,39 @@
+import os
+
+os.environ.setdefault("APP_BASE_URL", "http://testserver")
+os.environ.setdefault("APP_SECRET_KEY", "test-secret")
+os.environ.setdefault("TOKEN_ENCRYPTION_KEY", "y-KaYJS2O-CziGFYfjtMObHX73xMI9FwFipMnFpHKAY=")
+os.environ.setdefault("DATABASE_URL", "postgresql+psycopg://test:test@localhost/test")
+os.environ.setdefault("ALLOWED_GOOGLE_EMAIL", "owner@example.com")
+
+import pytest
+from sqlalchemy import create_engine, event
+from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import StaticPool
+
+from app.db import Base
+from app import models  # noqa: F401
+
+
+@pytest.fixture
+def db_session():
+    engine = create_engine(
+        "sqlite:///:memory:",
+        connect_args={"check_same_thread": False},
+        poolclass=StaticPool,
+    )
+
+    @event.listens_for(engine, "connect")
+    def _enable_sqlite_fk(dbapi_connection, _):
+        cursor = dbapi_connection.cursor()
+        cursor.execute("PRAGMA foreign_keys=ON")
+        cursor.close()
+
+    Base.metadata.create_all(engine)
+    session_factory = sessionmaker(bind=engine, autoflush=False, autocommit=False)
+    session = session_factory()
+    try:
+        yield session
+    finally:
+        session.close()
+        engine.dispose()