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.lock

@@ -238,14 +238,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.0.0"
-  flutter_markdown:
+  flutter_markdown_plus:
     dependency: "direct main"
     description:
-      name: flutter_markdown
-      sha256: "08fb8315236099ff8e90cb87bb2b935e0a724a3af1623000a9cec930468e0f27"
+      name: flutter_markdown_plus
+      sha256: "039177906850278e8fb1cd364115ee0a46281135932fa8ecea8455522166d2de"
       url: "https://pub.dev"
     source: hosted
-    version: "0.7.7+1"
+    version: "1.0.7"
   flutter_riverpod:
     dependency: "direct main"
     description: