feat(library): add upload button next to search/filter

Commit notes

- Add upload icon button (Plus) to LibrarySearchFilter component - Hidden file input accepts multiple audio files (wav, mp3, flac, m4a, aac, aiff, ogg) - Upload button triggers file picker on click - Handle file selection in library page using existing upload mutation - Upload progress displayed via existing UploadProgressPanel - Works on all devices with accessible button styling and touch targets

Co-authored-by: armin.naimi <[email redacted]>