feat(map): add open-source map block (MapLibre GL + OpenFreeMap)

Single-location + multi-marker, side-by-side and map-only layouts.
Zero-config — no API key. MapLibre is vendored via vite and loaded
conditionally when a page contains a map block. Provider resolution
is a single switchable function so other tile providers can be added
later without changing the block contract.

package.json

@@ -16,6 +16,7 @@
   "dependencies": {
     "alpinejs": "^3.15.0",
     "katex": "^0.16.22",
+    "maplibre-gl": "^4.7.1",
     "markmap-autoloader": "^0.18.12",
     "medium-zoom": "^1.0.8",
     "mermaid": "^11.12.0",
@@ -40,7 +41,7 @@
     "update:starters": "poetry run python ./scripts/update.py",
     "vendor:libs": "vite build --config vite.config.js",
     "vendor:libs:watch": "vite build --config vite.config.js --watch",
-    "vendor:update-and-build": "pnpm up katex mermaid markmap-autoloader alpinejs plotly.js preact --latest && pnpm vendor:libs",
+    "vendor:update-and-build": "pnpm up katex mermaid markmap-autoloader alpinejs plotly.js preact maplibre-gl --latest && pnpm vendor:libs",
     "test:releaser": "poetry run python scripts/test_release_modules.py",
     "check:template-deps": "node scripts/check-template-deps.mjs"
   },