Add OpenSeaMap / OpenSnowMap overlay layers (#10)

Two independently toggleable open-data raster overlays — OpenSeaMap
sea marks (buoys, lighthouses, ports) and OpenSnowMap ski pistes —
drawn as Cesium.ImageryLayers directly on the Cesium globe surface.
Same "small array of descriptors" shape as MAP_STACKS in
mapStackController.js.

Visible on the osm/bing-aerial/bing-labels map stacks and invisible
(not broken — the layer's stats say so in plain text) on the default
photoreal stack, since Google Photorealistic 3D Tiles render with the
globe hidden.

OpenRailwayMap and OpenInfraMap, also requested in #10, are
deliberately NOT included in this pass: OpenRailwayMap's public tile
server enforces a Referer allowlist scoped to its own site (confirmed
by direct request — every other Referer, including none, 403s), and
OpenInfraMap serves MapLibre GL vector tiles, not raster XYZ — that
would need a genuine vector-tile rendering pipeline, not a
Cesium.ImageryLayer drop-in. Worth its own dedicated pass.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

src/voice/gevActions.js

@@ -176,6 +176,16 @@ const LAYER_ALIASES = new Map([
   ['firms', 'local-firms'],
   ['fires', 'local-firms'],
   ['active fires', 'local-firms'],
+  ['map overlays', 'osm-overlays'],
+  ['open map overlays', 'osm-overlays'],
+  ['sea marks', 'osm-overlays'],
+  ['seamarks', 'osm-overlays'],
+  ['nautical charts', 'osm-overlays'],
+  ['openseamap', 'osm-overlays'],
+  ['ski pistes', 'osm-overlays'],
+  ['ski slopes', 'osm-overlays'],
+  ['snow map', 'osm-overlays'],
+  ['opensnowmap', 'osm-overlays'],
 ]);
 
 const CITY_ALIASES = new Map([