Update Audience Notes

Workflow

At end of weekly pipeline:
- [ ] Step 1: Review attribution outputs for any pattern observed
- [ ] Step 2: Filter to confidence ≥ medium only (low is never appended)
- [ ] Step 3: Format as YAML block per schema
- [ ] Step 4: Append to shared-context/audience-notes.md
- [ ] Step 5: If no medium+ observation this week, log "no additions this week" to weekly report's data-caveats (not to audience-notes)

YAML block schema