Update typedoc to 0.28 for TypeScript 5.9 support

typedoc 0.27 peer-depends on typescript <=5.8.x, so the lockfile-only
bump to typescript 5.9.3 in the previous commit left the tree
inconsistent and npm ci refused to install it.

Author: microbit-matt-hillsdon

package-lock.json

@@ -83,7 +83,7 @@
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "storybook": "^10.5.10",
-    "typedoc": "^0.27.6",
+    "typedoc": "^0.28.20",
     "typescript": "^5.2.2"
   }
 }