Refactor the admin storage backend creation and editing flows to use
provider-specific pages (e.g., `/admin/storage/new/sftp`) instead of a
single generic form. This ensures only relevant fields are rendered for
each storage provider (such as SFTP, S3, or WebDAV).
Additionally:
- Prevent mutation of the storage provider type during backend edits.
- Add comprehensive unit tests for provider-specific rendering, edit
validation, and CSRF/admin route protection.
Implement a new card-based UI for managing storage backends in the admin panel. This update improves the visual presentation and usability of the storage configuration page.
Key changes:
- Added comprehensive CSS styles for storage cards, including status indicators, metadata layouts, and action buttons.
- Updated the storage admin template to render storage configurations as cards with type-specific details (Local, S3, SFTP, SMB, WebDAV).
- Integrated inline actions for testing, editing, disabling, and deleting storage backends.
- Enhanced sidebar link alignment with flexbox.
- Introduce S3-compatible storage backend support using minio-go.
- Add configuration options for local storage limits, box limits, and rate limiting.
- Implement storage backend selection (local vs S3) for anonymous and registered users.
- Add an `/admin/storage` management interface.
- Update documentation and environment examples with the new configuration variables.
