- l3-backend-3b: extend DocumentController description to include the
per-month density aggregation endpoint.
- l3-frontend-3b: add /documents/+page.ts (client-side gated loader) and
TimelineDensityFilter component, plus relationships to the density
endpoint and the search dashboard.
Per Markus' follow-up §5: both diagrams are mandatory before merge.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>