Replace source/license links with website link on About screen

Remove the source-code link and AGPL license row, and point users to
the project website (https://oott-security.net) instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/test/widget/about_test.dart

@@ -19,7 +19,10 @@ void main() {
     // Assert the fallback prefix only, not the release date literal (it changes
     // every release).
     expect(find.textContaining('Released'), findsOneWidget);
-    expect(find.text('Source code'), findsOneWidget);
+    expect(
+      find.text('Check out our website and Git repo here'),
+      findsOneWidget,
+    );
     expect(find.text('openssl'), findsOneWidget);
   });
 }