Patch Morocco geometry in Equal Earth MapLibre style

[kylemcdonald]

Note: these code changes and PR were generated by GPT-5.5 but I reviewed them manually. This PR responds to an issue I ran into with Morocco/Western Sahara while building https://ews.kylemcdonald.net/

Summary

• add supplemental Morocco/Western Sahara fill and coastline GeoJSON derived from the hosted z6 Equal Earth vector tiles
• update the MapLibre Natural Earth countries style to draw the supplemental geometry and suppress the broken MAR/SAH country fill/outline from the lower-zoom vector tiles
• document why the patch uses tile-derived coordinates instead of raw Natural Earth coordinates

Context

The hosted ne_extracts_8857 vector tiles currently omit part of southern Morocco / Western Sahara at lower zooms, while the max-zoom tiles include usable geometry. Deriving this patch from the same z6 tiles keeps it aligned with the existing Equal Earth-in-MapLibre rendering and avoids duplicated land-border strokes.

Validation

• jq empty static/natural-earth-countries-style.json
• MapLibre style validation via @maplibre/maplibre-gl-style-spec