feat(maps): add MapLibre OpenFreeMap support (#1317)

Adds MapLibre GL with OpenFreeMap as a tokenless third map provider
alongside Leaflet and Mapbox: a provider abstraction with style presets,
CSP + service-worker entries for tiles.openfreemap.org, and the
map_provider allow-list entry. Mapbox-only APIs stay gated behind the
mapbox provider, and existing Mapbox/Leaflet users are unaffected.

Maintainer review follow-ups folded in: the new map-settings strings are
translated across all locales; the GL engine is lazy-loaded so
Leaflet-only installs don't download it; MapLibre gets its own
maplibre_style slot so switching providers no longer overwrites a custom
Mapbox style; and the MapLibre render path plus the OpenFreeMap
style-guards are covered by tests.

client/src/types.ts

@@ -118,9 +118,10 @@ export interface Settings {
   map_booking_labels?: boolean
   map_poi_pill_enabled?: boolean
   optimize_from_accommodation?: boolean
-  map_provider?: 'leaflet' | 'mapbox-gl'
+  map_provider?: 'leaflet' | 'mapbox-gl' | 'maplibre-gl'
   mapbox_access_token?: string
   mapbox_style?: string
+  maplibre_style?: string
   mapbox_3d_enabled?: boolean
   mapbox_quality_mode?: boolean
 }