Add AT Protocol publishing, media support, and SQLite stability

Publishing:
- Add publisher.go for posting feed items to AT Protocol PDS
- Support deterministic rkeys from SHA256(guid + discoveredAt)
- Handle multiple URLs in posts with facets for each link
- Image embed support (app.bsky.embed.images) for up to 4 images
- External embed with thumbnail fallback
- Podcast/audio enclosure URLs included in post text

Media extraction:
- Parse RSS enclosures (audio, video, images)
- Extract Media RSS content and thumbnails
- Extract images from HTML content in descriptions
- Store enclosure and imageUrls in items table

SQLite stability improvements:
- Add synchronous=NORMAL and wal_autocheckpoint pragmas
- Connection pool tuning (idle conns, max lifetime)
- Periodic WAL checkpoint every 5 minutes
- Hourly integrity checks with PRAGMA quick_check
- Daily hot backup via VACUUM INTO
- Docker stop_grace_period: 30s for graceful shutdown

Dashboard:
- Feed publishing UI and API endpoints
- Account creation with invite codes

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

docker-compose.yml

@@ -3,6 +3,7 @@ services:
     build: .
     container_name: app-1440-news
     restart: unless-stopped
+    stop_grace_period: 30s
     env_file:
       - pds.env
     volumes: