P5-01: Audio file slot

[socialawy]

Summary

Add a single audio track reference to the sequence spec and Composer UI, allowing users to attach an audio file to their sequence.

Acceptance Criteria

• Schema extension: Add audio field to sequence.json schema:

  "audio": {
    "src": "string",
    "offset": 0,
    "volume": 1.0
  }

  • src: filename/reference to audio file
  • offset: seconds into the sequence where audio starts (default 0)
  • volume: 0.0–1.0 (default 1.0)
  • Field is optional (sequences without audio remain valid)
• Composer UI: Audio slot panel with:
  • File picker accepting .mp3, .wav, .ogg
  • Display of selected file name
  • Remove audio button
• IndexedDB storage: Audio file stored as Blob in IndexedDB alongside the project (uses persistence from P5-10)
• Waveform visualization: Canvas2D waveform display in the timeline area showing the audio shape
• Mute/unmute toggle in the audio panel

Tests (Vitest)

• Schema validation passes with audio field present
• Schema validation passes without audio field (backward compatible)
• Audio file loading: mock file → stored as blob → retrievable
• Volume defaults to 1.0, offset defaults to 0 when not specified
• Waveform renderer receives correct audio data

Architecture Notes

• src/spec/ — Schema definition + validation for the audio field
• src/composer/ — Audio slot panel UI, waveform Canvas2D component
• src/store/ — Audio state in Zustand store + IndexedDB blob persistence
• Waveform uses Canvas2D (consistent with existing renderer approach)

Dependencies

• P5-10: Project save/load (IndexedDB) #12 (P5-10: Project save/load — for IndexedDB blob storage)

Priority

Phase 5, Item 01 — Jules priority queue position: 3