Add web map components and layer control extracted from ldproxy/ogcapi-html

[PZahnen]

Extracts the map components from ldproxy's ogcapi-html into reusable @xtramaps packages. This is the first half of the refactoring. The ldproxy side (ldproxy/ldproxy, branch migrate-web-map-components) consumes these packages and can only be merged once they are published.

New packages

• @xtramaps/web-map-maplibre / -react: MapLibre map component, rebuilt on @vis.gl/react-maplibre and maplibre-gl 6.4 (replaces the unmaintained react-maplibre-ui). Includes style/data-layer helpers, hover/click popups and CanvasOverlay.
• @xtramaps/layer-control-maplibre / -react: LayerControl with nested groups, radio groups and merge groups. Legend icons come from @xtramaps/legend-symbols-maplibre-react.
• @xtramaps/web-map-openlayers / -react: 1:1 migration onto rlayers 3.9 / ol 10.8. The globalThis._map bridge is replaced by a ref API.
• @xtramaps/web-map-cesium / -react: migrated onto @cesium/engine 26 / @cesium/widgets 16, with cleanup on unmount and error handling added.

Other changes

• Fixed style-load race conditions and a defaultStyle merge bug in the MapLibre component
• Storybook stories/tests for web-map-maplibre and layer-control-maplibre
• CI now runs npm run test
• Renovate: auto-merge policy for patch updates

Changesets for all new packages are included.

Open points

• Initial version numbers: the new packages are already at 1.0.0 in package.json and the changesets are minor, so the first published version would be 1.1.0.