refactor(audio): prune the orphaned TypeScript DSP modules

Commit notes

Verified that key-detection.ts, loop-detection.ts, superflux.ts, and cqt.ts form a closed, dead cluster: they reference only each other, nothing outside src/audio/ imports them, and the audio barrel's real consumers (worker, admin, pack-generator) only use ffmpeg/essentia-client symbols. The test suite uses its own local copies, not these modules.

These were the standalone DSP helpers behind the in-process analyzer removed in the previous commit, so they are now unreachable. Remove the four modules (~1730 lines), trim the audio barrel to ffmpeg + essentia-client, and drop the now-unused meyda / @types/meyda dependencies (loop-detection was the only user), refreshing the lockfile.

typecheck + lint clean; 68 audio/mapper unit tests pass; frozen-lockfile install verified.

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