refactor: Remove TypeScript audio analysis fallback

Commit notes

All audio analysis is now exclusively handled by Python/Essentia. If the service is unavailable, analysis fails with a clear error message.

Changes: - Remove TypeScript analyzer caching and fallback logic - analyzeAudioHybrid now throws if Essentia service unavailable - Update worker thread comment - Simplify code by removing unused fallback paths

This ensures: - Single source of truth for audio analysis - No hidden fallback behavior that could mask issues - Cleaner debugging (analysis either works or fails clearly)

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