## Summary
- Adds `public/geofilter-docs.html` — a self-contained, app-served
documentation page for the geofilter feature, matching the builder's
dark theme
- Updates the GeoFilter Builder's help-bar "Documentation" link from
GitHub markdown URL to the local `/geofilter-docs.html`
## Docs coverage
Polygon syntax, coordinate ordering (`[lat, lon]` — not GeoJSON `[lon,
lat]`), multi-polygon clarification (single polygon only), examples
(Belgium rectangle + irregular shape), legacy bounding box format, prune
script usage.
## Test plan
- [x] Open `/geofilter-docs.html` — dark theme renders, all sections
visible
- [x] Open `/geofilter-builder.html` → click "Documentation" → navigates
to `/geofilter-docs.html` in same tab
- [x] Click "← GeoFilter Builder" on docs page → navigates back to
`/geofilter-builder.html`
Closes#820
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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
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