Switch edit_release to read from tags instead of cache (#45)

[devin-ai-integration]

Summary

Closes #45.

edit_release previously built the editable TOML via MetadataRelease.from_cache(release, tracks), presenting the readonly cache's derived view in the write path. It now reads AudioTags.from_file for each track and builds the TOML with a new MetadataRelease.from_audiotags(release, tracks, audiotags):

• Release-level audio fields (title, releasetype, dates, edition, catalognumber, labels, genres, secondary genres, descriptors, release artists) come from the first track's AudioTags — consistent with how the cache derives release-level tags from the first track.
• Per-track fields (discnumber, tracknumber, title, artists) come from each track's AudioTags.
• new, favorite, and rating remain sourced from the cached Release, since they live in the .rose.{id}.toml datafile rather than audio tags.

from_cache had no other callers and is removed. The initial update_cache_for_releases call is kept so source paths stay fresh.

Adds a regression test asserting the editable TOML reflects on-disk tag changes even when the cache update is a no-op.

Link to Devin session: https://app.devin.ai/sessions/e54bb0f1aadc4db994169ae3e8e14cba
Requested by: @azuline

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.