refactor(audio): make formats explicit

[flamboh]

What changed

• add authoritative AudioFormat identity to every TagiumFile
• centralize MP3 extension, MIME, admission hint, filename, and output helpers
• route hard-coded naming behavior through the format module across import, editor, cleanup, hydration, and export
• keep metadata parsing/writing behind the existing AudioMetadataIO seam with no premature adapter registry
• add format-helper and metadata-I/O seam coverage for misleading MIME/extensions and filename preservation

Why

FLAC support needs format identity and naming rules to be explicit before a second format can safely enter the system. This PR is behavior-preserving for MP3 and does not add or advertise FLAC.

Verification

• bun run typecheck
• bun run lint
• 322 unit tests passed
• 78 focused affected tests passed
• two fresh independent reviews passed with no findings
• full suite reached 393 passing; 6 server proxy tests could not bind 127.0.0.1 in the sandbox (EPERM)
• git diff --check

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	tagium	3e2721e	Commit Preview URL Branch Preview URL	Jul 17 2026, 01:24 PM

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit 3e2721e.}

[flamboh]

• feat(audio): add waveform preview playback #127
• feat(ui): add mobile workspace navigation #125
• feat(export): confirm bulk downloads #123
• feat(metadata): reopen cleanup suggestions #121
• feat(ui): polish workspace states #120
• feat(metadata): add advanced editor #124
• feat(metadata): add advanced field policy #122
• refactor(audio): make formats explicit #119 👈 (View in Graphite)
• main

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[flamboh]

Superseded by #129, which merged the current lossless multi-format metadata engine.