feat(uploads): add native resumable upload support

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.

scripts/env/dev.env.example

@@ -9,6 +9,9 @@ WARPBOX_CLEANUP_ENABLED=true
 WARPBOX_CLEANUP_EVERY=1h
 WARPBOX_THUMBNAIL_ENABLED=true
 WARPBOX_THUMBNAIL_EVERY=1m
+WARPBOX_RESUMABLE_UPLOADS_ENABLED=true
+WARPBOX_RESUMABLE_CHUNK_MB=16
+WARPBOX_RESUMABLE_RETENTION_HOURS=1
 WARPBOX_MAX_UPLOAD_SIZE_MB=16384
 WARPBOX_ANONYMOUS_UPLOADS_ENABLED=true
 WARPBOX_ANONYMOUS_MAX_UPLOAD_MB=512