Replaces local filesystem document storage with S3-compatible object storage.
Adds embedded SeaweedFS 'weed mini' for local development and Docker deployments.
Updates document upload flow to use presigned URLs with a server fallback proxy.
Refactors auth configuration to use BASE_URL and AUTH_SECRET.
BREAKING CHANGE: Renamed BETTER_AUTH_URL to BASE_URL and BETTER_AUTH_SECRET to AUTH_SECRET. Removed legacy document upload/content endpoints. Requires S3 environment variables (auto-configured for embedded SeaweedFS).
- Replace client-side IndexedDB with server-first document storage
- Add document caching layer for offline capability and performance
- Implement document transfer during anonymous-to-authenticated account linking
- Add database indexes for improved query performance
- Update document contexts to use new caching system
- Refactor document upload and deletion APIs
- Add audiobook pruning for missing files
- Improve test isolation with namespace support
- Add unit tests for document cache and transfer functions
