feat: enhance audio processing events and UI feedback

Commit notes

- Added detailed event handling for audio processing stages, including success and failure notifications. - Introduced a new ProcessingStatusIndicator component to visually represent processing states in the UI. - Updated backend event emissions to include processing stages for better tracking. - Enhanced library routes to support new error and analysis status fields.

Files modified: - backend/src/worker.ts - backend/src/routes/library.ts - backend/src/routes/upload-links.ts - backend/src/services/library-events.ts - frontend/src/lib/components/ProcessingStatusIndicator.svelte - frontend/src/lib/hooks/useLibrarySSE.svelte.ts - frontend/src/routes/library/+page.svelte - frontend/src/routes/library/components/LibrarySampleGrid.svelte