fix: correct contract test JS references and update stats API baseline
The contract test had invented "friendly" JS alias names (e.g., total_audio_duration)
but dashboard.js uses the Python field names directly (e.g., total_transcript_duration).
Fixed all 9 mismatched JS references. Also regenerated the stats API baseline to match
the current v2 schema structure.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>