feat(audio-tab): full audio track inspector with meters, mute/solo, faders
Issue #80 — replaces the stub AudioTab (two static waveforms) with a
broadcast-ops-grade audio panel:
- DB: add audio_metadata JSONB column to assets (migration 022)
- Worker: getMediaInfo now extracts per-stream audio metadata
(codec, channels, channel_layout, sample_rate, bit_depth, bit_rate,
language, title, disposition)
- Worker: proxy job persists audio_metadata into the assets row
- API: new GET /assets/:id/audio returns structured track list
- Frontend AudioTab: per-track rows with:
- Track name/index with language badge
- SVG waveform per track (color-coded)
- L/R level meters via Web Audio API AnalyserNode
- Per-track metadata row (codec, layout, sample rate, bit depth, bitrate)
- Mute / Solo buttons with proper solo-logic
- Per-track volume fader
- Master section with summed L/R meters and master fader
- MetadataTab: show audio track summary when audio_metadata present
- CSS: full audio-tab layout, responsive collapse at 900px