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>

compose.yml

@@ -0,0 +1,35 @@
+services:
+  app:
+    build: .
+    restart: unless-stopped
+    env_file:
+      - .env
+    ports:
+      - "8080:8080"
+    depends_on:
+      postgres:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD", "curl", "-f", "http://127.0.0.1:8080/api/health"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 10s
+
+  postgres:
+    image: postgres:16
+    restart: unless-stopped
+    environment:
+      POSTGRES_DB: youtube_app
+      POSTGRES_USER: youtube_app
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U youtube_app -d youtube_app"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+volumes:
+  postgres_data: