spike(world-map): OpenFreeMap vector dark basemap (#7077) — parked

[wcjord]

Parked spike for #7077 (dark-map contrast + water). NOT for merge yet — punting on the vector approach for now; this branch preserves the working integration so it can be picked up later.

What this does

Replaces the dark basemap (CartoDB Dark Matter raster) with OpenFreeMap VECTOR tiles, styled client-side, so label contrast + water are ours with a single request. Light mode stays OSM raster. The CartoDB raster is kept as an automatic fallback while the vector style loads / if it errors.

• pubspec.yaml: vector_map_tiles: 9.0.0-beta.9 (pinned exact — only the 9.x prerelease is compatible with our flutter_map ^8.2.2; stable 8.x needs flutter_map 7, and 10.x needs Flutter main + Impeller).
• world_map.dart: WorldMapController.darkMapStyle loads the OpenFreeMap dark style once.
• world_map_view.dart: dark base layer is a FutureBuilder<Style> → VectorTileLayer (default raster layerMode so each tile is rasterized once + blitted), raster fallback otherwise; attribution updated to OpenMapTiles.

What's confirmed

• Co-resolves with flutter_map/flutter_map_marker_cluster 8.2.2 and compiles for Flutter web (the key unknown).
• OpenFreeMap style + tilejson endpoints are live, valid, key-less, commercial-OK.

Why it's parked

• Slow to resolve + unproven web perf. vector_map_tiles does not list Web as a supported platform (web support is an open "help wanted" effort); on CanvasKit the initial style+tile resolve is noticeably slow, and parse/paint can land on the UI thread alongside the marker-cluster repaints. Under throttling the cost is real, and we don't yet have a representative perf picture across our actual device mix.
• Prerelease dependency (9.0.0-beta.9).

To resume

The integration is complete; the open problem is web rendering cost. Options to revisit: self-host OpenFreeMap tiles, tune the vector layer (concurrency / raster mode / tile delay), restyle the OpenFreeMap dark style (water + label colors — it ships "not yet complete"), handle the ne2_shaded raster relief source, and benchmark against real device analytics before flipping it on. Or fall back to the Stadia raster stopgap if a quicker contrast/water win is wanted.

[coderabbitai]

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