refactor(audio): remove the dead in-process TypeScript DSP engine

Commit notes

The legacy TypeScript analysis path (analyzeAudioWithTypeScript / analyzeAudioWithTypeScriptFromFile) and its entire DSP stack — BPM/beat tracking, key detection, LUFS, spectral features, loop detection, transients, the heuristic drum classifier, and MFCC embedding — were fully superseded by the Essentia microservice and CLAP zero-shot classification. They were unreferenced by every live entry point (which delegate to Essentia), so this was pure dead code: ~3150 lines.

audio-analysis.ts now just delegates analysis to Essentia and layers the optional LLM categorization pass on top. Removed the orphaned imports (meyda, bun $, key-detection/loop-detection/superflux helpers) and refreshed the module header.

No behavior change: the live paths (analyzeAudio, analyzeAudioFromFile, analyzeAudioFromFileWorker, analyzeAudioFromS3Key, analyzeAudioFull, categorizeWithLLM) are untouched, and all unit tests pass.

Co-Authored-By: Claude Opus 4.8 <[email redacted]> Claude-Session: [private session redacted]