Feature request: Expose Spotify audio features API to Studio agent

[sjamaniel]

Studio's AI agent (Kit) has deep Spotify integration for playback, library, and search — but lacks access to audio features like key, BPM, energy, danceability, and valence. These are already available via Spotify's /audio-features endpoint, but not exposed through the Studio CLI.

Why this matters:
I've been using Studio to curate psychedelic meditation journeys — carefully sequenced playlists where harmonic mixing is essential. The agent can restructure playlists, suggest tracks, and reason about musical flow, but has to guess at key and energy because it can't read the actual values Spotify already has.

Request:
Add audio feature data (at minimum: key, mode, BPM, energy, valence) to spotify_cli track metadata output. This would unlock:

Harmonic mixing assistance (Camelot Wheel sequencing)
Energy arc analysis across a playlist
Mood-aware curation grounded in real data, not guesswork

The data exists. The agent just can't see it. Connecting these two would make Studio genuinely powerful for intentional listening design.