feat(countries): replace Map view with browse-by-country (like Tags)

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>

web/package.json

@@ -30,7 +30,6 @@
 		"bits-ui": "^2.18.1",
 		"clsx": "^2.1.1",
 		"lucide-svelte": "^1.0.1",
-		"maplibre-gl": "^5.24.0",
 		"mode-watcher": "^1.1.0",
 		"svelte-sonner": "^1.1.1",
 		"tailwind-merge": "^3.6.0",