- Add public/logged_in/private visibility levels to songs and playlists via database migration (002_visibility.sql)
- Replace old `is_public` boolean with new `visibility` enum in admin forms, API schemas, and services
- Implement access control logic:
- Guests see only public items that don't contain restricted tracks
- Logged-in users see public + logged_in items (excluding private ones)
- Admins see all; regular users manage their own content
- Auto-upgrade playlist visibility when adding more restrictive songs
- Add UI badges for visibility levels and update admin views to reflect new hierarchy
PWA enhancements:
- Update web manifest with proper name, colors, and icon paths
- Add service worker (sw.js) with cache-first for static assets and network-first for HTML
- Register SW at root (/sw.js) with Service-Worker-Allowed header for full origin scope
- Add theme-color meta tag and navigate.js for client-side routing
Other:
- Update admin nav label from "Admin" to "My Music" to reflect role-based access
