Migrate flutter_markdown → flutter_markdown_plus; fix app label

flutter_markdown was discontinued; flutter_markdown_plus is the
maintained drop-in replacement (same API, updated imports only).

Also set android:label to "Fabled" so the app appears correctly
on the home screen and in the app drawer instead of "fabled_app".

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pubspec.yaml

@@ -19,11 +19,11 @@ dependencies:
   dio_cookie_manager: ^3.1.1
   path_provider: ^2.1.4
   shared_preferences: ^2.3.2
-  flutter_markdown: ^0.7.3
   markdown: ^7.2.2
   package_info_plus: ^8.0.0
   open_file: ^3.3.2
   flutter_inappwebview: ^6.1.5
+  flutter_markdown_plus: ^1.0.7
 
 dev_dependencies:
   flutter_test: