build(deps): update markdown-it to 15.0.2

markdown-it 15 ships its own type declarations, so @types/markdown-it is dropped.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -67,9 +67,8 @@
     "@angular/platform-server": "^22.2.1",
     "@angular/router": "^22.2.1",
     "@angular/ssr": "^22.2.1",
-    "@types/markdown-it": "^14.1.2",
     "express": "^5.2.1",
-    "markdown-it": "^14.1.1",
+    "markdown-it": "^15.0.2",
     "rxjs": "~7.8.0",
     "tslib": "^2.3.0",
     "zone.js": "~0.16.2"