* feat(maps): add regional map downloads via go-pmtiles extract
* address Copilot review feedback on PR #780
- auto-refresh preflight on selection/maxzoom change with 400ms debounce and
requestId stale-safety so the confirm button no longer requires a two-step
"Estimate Size" -> "Start Download" dance
- safeUpdateProgress helper replaces fire-and-forget updateProgress().catch()
pattern so cancelled-job errors (code -1) can't surface as unhandled rejections
- gate world basemap source on worldBasemapReady - when ensureWorldBasemap()
fails we already delete world.pmtiles, so emitting the source was producing
404s on every tile request
- verify go-pmtiles binary SHA256 at image build time; upstream doesn't ship a
checksums file so per-arch hashes are pinned as build args with a regenerate
note when bumping PMTILES_VERSION
0xGlitch