fix(map): use a fontstack the glyph server actually serves

[bardesss]

Problem

Every symbol layer we add ourselves asked for ["Open Sans Bold"]. The glyph server declared in resolveMapStyle's raster fallback does not host that stack:

Open Sans Bold         HTTP 404
Open Sans Regular      HTTP 404
Open Sans Semibold     HTTP 200
Noto Sans Regular      HTTP 200

So the glyph request 404s and the labels never render — cluster counts on the main map, and node numbers plus start/end markers on the route map.

Only the raster path is affected. The default Carto vector style ships its own glyph server, which does serve Bold, so labels render there and the breakage is invisible unless map_tile_url points at a {z}/{x}/{y} raster template.

Fix

Carto serves Semibold too:

Fontstack	demotiles (raster fallback)	Carto (default vector)
Open Sans Bold	404	200
Open Sans Semibold	200	200

That makes Semibold the one stack that works against either glyph server. Hoisted to a MAP_FONT constant next to the GLYPHS URL that constrains it — the two must move together — and replaces all four literals (1 in MapView, 3 in RouteMap).

The visible change on the vector path is cluster-count and route-label weight going from Bold to Semibold.

Verification

• tsc -b clean; 523 tests across 108 files pass (522 before — one added).
• New test in style.test.ts asserts MAP_FONT is a stack the glyph host actually serves, so this can't silently regress.