Features:
- Gallery upload, delete, reorder (drag & drop)
- Preview images in admin panel
- Same upload flow as events (WebP conversion via sharp)
- Complete system documentation explaining:
- Architecture (Frontend/Backend/Volume)
- Upload flow (Multipart → Sharp → WebP → Storage)
- Why SQLite works on Fly.io (persistent volumes)
- Troubleshooting guide
Admin now has full CRUD for both Events and Gallery!
