Add GeoMap fences with interactive maps and feature tables

[asafmor]

geomap Markdown fences now render an interactive Leaflet map and an expandable feature table in the generated single HTML file. The table acts as an index: selecting a row reveals its layer, focuses and highlights the feature, and opens its popup. Map clicks stay local and never scroll to or expand the table.

• Validate and normalize GeoJSON once per fence, isolate malformed layers, and keep one row per Feature even for large route tracks.
• Support all standard geometry types, independent layer toggles, combined initial bounds, category markers, route patterns, selection, hover, search, and safe provenance links.
• Add a narrow, icon-only Google Maps column for Point coordinates. Links use latitude/longitude order and never trigger row selection.
• Keep feature tables usable if Leaflet fails to load, include them in print output, and clean up maps during document navigation.
• Separate validation, DOM/table rendering, map behavior, styling, and CDN loading into small modules. Inline the component into the packaged template; load pinned Leaflet assets with integrity checks only when maps appear.

Includes a GeoMap guide and runnable Markdown example. Map assets and tiles require internet access; Markdown retains its existing Markdown-it CDN dependency.

Validation: all 48 tests pass; npm pack --dry-run --ignore-scripts passes. Browser checks in Chromium and WebKit mobile emulation covered live CDN rendering, table-only navigation, independent external links, touch/keyboard interaction, narrow-screen layout, all five themes, multiple maps, page navigation, printing, filtering, a 12,000-coordinate route, hostile property text, and the blocked-CDN fallback.