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>

api/src/rehearsalhub/db/models.py

@@ -232,6 +232,8 @@ class AudioVersion(Base):
     nc_file_etag: Mapped[Optional[str]] = mapped_column(String(255))
     cdn_hls_base: Mapped[Optional[str]] = mapped_column(Text)
     waveform_url: Mapped[Optional[str]] = mapped_column(Text)
+    waveform_peaks: Mapped[Optional[list]] = mapped_column(JSONB)
+    waveform_peaks_mini: Mapped[Optional[list]] = mapped_column(JSONB)
     duration_ms: Mapped[Optional[int]] = mapped_column(Integer)
     format: Mapped[Optional[str]] = mapped_column(String(10))
     file_size_bytes: Mapped[Optional[int]] = mapped_column(BigInteger)