Add --reprocess option to observe-sense for batch re-analysis
New CLI options for observe-sense:
- --reprocess {screen,audio,all}: Delete existing outputs and reprocess
- --segment HHMMSS_LEN: Filter to specific segment
- --dry-run: Preview what would be deleted without making changes
The reprocess flow deletes matching .jsonl outputs, then runs normal
batch processing. Emits observe.observed events per segment, which
triggers supervisor's segment dream pipeline automatically.
Also fixes scan_day() to use AUDIO_EXTENSIONS constant instead of
hardcoded tuple, and adds segment format validation in CLI.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>