feat(map): default to our own style with light + dark variants

Switch the default base map from MapTiler's proprietary style to OpenMapX's
own style — a recolored OSM Bright derivative — so the default no longer
depends on MapTiler's "style only with MapTiler tiles" terms.

- add a dark map style (openmapx-dark.json) generated from the light style by
  scripts/generate-dark-map-style.mjs (re-runnable; road network lifted for
  contrast, shields keep their fixed sprite-background text colours)
- loadOpenMapXStyle is theme-aware; MapCanvas, the offline maps, the place
  mini-map and the offline download all load the light/dark variant
- default styleProvider flips to "openmapx"; the MapTiler style stays a
  non-default opt-in
- attribution follows the data flow: OpenStreetMap (data) + OpenMapTiles (our
  OSM-Bright-derived style: CC-BY design + schema) always, plus MapTiler when
  their hosted tiles are used
- record the OSM Bright notice (BSD-3 code + CC-BY-4.0 design) in LICENSING.md
  and on the /licenses page

Author: Medformatik

LICENSING.md

@@ -26,6 +26,25 @@ may include the Apache-2.0 libraries, but not the other way around. That is why
 the SDK and shared libraries — the parts we want others to reuse — are the
 permissive ones, and the product that ties them together is copyleft.
 
+## Bundled map style
+
+The default map style (`apps/web/public/styles/openmapx-streets.json` and its
+dark variant `openmapx-dark.json`, generated by
+`apps/web/scripts/generate-dark-map-style.mjs`) is a **recolored derivative of
+OSM Bright** ([`openmaptiles/osm-bright-gl-style`](https://github.com/openmaptiles/osm-bright-gl-style)),
+itself derived from Mapbox Open Styles. OSM Bright is dual-licensed:
+
+| Part | License | Obligation |
+|---|---|---|
+| Style **code** (layer/expression JSON) | **BSD-3-Clause** | Retain the copyright notice (shipped on the [`/licenses`](apps/web/src/app/(legal)/licenses) page); no endorsement use of the names. |
+| Style **design** ("look and feel") | **CC-BY-4.0** | Visibly credit **“© OpenMapTiles”** (linking to <https://openmaptiles.org/>) on maps derived from it, alongside **“© OpenStreetMap contributors”**. |
+
+OpenMapX satisfies the CC-BY design attribution through the map's attribution
+control (`BaseAttributions` / `baseMapVectorCredits` in `apps/web`), which shows
+“© OpenMapTiles” and “© OpenStreetMap contributors” on every vector base map —
+plus “© MapTiler” when MapTiler's hosted tiles are used. The full upstream
+notice text is reproduced on the `/licenses` page.
+
 ## Contributing and relicensing
 
 Contributions are accepted under a Contributor License Agreement