feat(waveform): precompute and store peaks in DB for instant rendering

Store waveform peaks inline in audio_versions (JSONB columns) so WaveSurfer
can render the waveform immediately on page load without waiting for audio
decode. Adds a 100-point mini-waveform for version selector thumbnails.

Backend:
- Migration 0006: adds waveform_peaks and waveform_peaks_mini JSONB columns
- Worker generates both resolutions (500-pt full, 100-pt mini) during transcode
  and stores them directly in DB — replaces file-based waveform_url approach
- AudioVersionRead schema exposes both fields inline (no extra HTTP round-trip)
- GET /versions/{id}/waveform reads from DB; adds ?resolution=mini support

Frontend:
- audioService.initialize() accepts peaks and calls ws.load(url, Float32Array)
  so waveform renders instantly without audio decode
- useWaveform hook threads peaks option through to audioService
- PlayerPanel passes waveform_peaks from the active version to the hook
- New MiniWaveform SVG component (no WaveSurfer) renders mini peaks in the
  version selector buttons

Fix: docker-compose.dev.yml now runs alembic upgrade head before starting
the API server, so a fresh volume gets the full schema automatically.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.dev.yml

@@ -25,6 +25,7 @@ services:
     build:
       context: ./api
       target: development
+    command: sh -c "alembic upgrade head && python3 -m uvicorn rehearsalhub.main:app --host 0.0.0.0 --port 8000 --reload"
     environment:
       DATABASE_URL: postgresql+asyncpg://${POSTGRES_USER:-rh_user}:${POSTGRES_PASSWORD:-default_secure_password}@db:5432/${POSTGRES_DB:-rehearsalhub}
       NEXTCLOUD_URL: ${NEXTCLOUD_URL:-https://cloud.example.com}