Removes the maplibre-gl Map view and adds "Countries" as a sixth
TagCategory, reusing the existing /tags/[category]/[[value]] browse
machinery instead of a bespoke map UI. Backed by a new self-contained
sidecar endpoint that aggregates photos.photo_country with BasePath
scoping, mirroring handleLabels/handleScopedCounts.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
