This commit restructures the audiobook generation and serving layer to rely exclusively on S3-compatible blob storage, removing the dependency on local filesystem paths.
- Bundle `ffmpeg` and `ffprobe` binaries via npm to ensure portability across environments.
- Update API routes to stream audio directly from blob storage instead of local disk.
- Remove legacy migration endpoints and filesystem-based indexing logic.
- Add startup scripts to facilitate the transition from local to remote storage.
BREAKING CHANGE: Audiobook functionality is now strictly dependent on S3 configuration. The previous filesystem-based storage method has been removed.
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).
