Implement a native chunked resumable upload API and frontend integration
to support reliable large file uploads.
Changes include:
- Added a 3-step resumable upload API flow (create session, upload chunks, complete session).
- Introduced configuration options for chunk size, retention hours, and toggling the feature.
- Updated the frontend to utilize resumable uploads with progress tracking.
- Configured temporary chunk storage under `data/tmp/uploads` with automatic cleanup.
- Documented the API flow and configuration in the README.
- Implement dynamic expiry options on the upload page based on user roles and retention policies.
- Add helper functions to build and format expiry options into human-readable labels.
- Introduce a new modern theme featuring glassmorphism, gradients, and frosted glass cards.
Modify the authentication handler to return an unauthorized error when
an invalid or disabled bearer token is provided, rather than silently
falling back to an anonymous request.
This ensures that clients attempting to authenticate but failing (due to
expired, malformed, or disabled tokens) are explicitly notified of the
auth failure instead of proceeding anonymously. True anonymous requests
without any Authorization header remain supported.
