fix: resolve non_exhaustive_switch_statement

src/kaiteki/lib/ui/main/main_screen.dart

@@ -454,8 +454,9 @@ class _MainScreenState extends ConsumerState<MainScreen> {
       case AppLocation.settings:
         context.push("/settings");
         break;
+      default:
+        return null;
     }
-    return null;
   }
 
   void _changePage(TabKind tab) => setState(() => _currentTab = tab);

src/kaiteki/lib/ui/shared/attachment_inspection_screen.dart

@@ -242,13 +242,13 @@ class _AttachmentInspectionScreenState
             ),
           ),
         );
+      default:
+        throw ArgumentError.value(
+          attachment.type,
+          "attachment",
+          "Can't build widget for specified attachment type",
+        );
     }
-
-    throw ArgumentError.value(
-      attachment.type,
-      "attachment",
-      "Can't build widget for specified attachment type",
-    );
   }
 
   Future<void> downloadAttachment(BuildContext context) async {

src/kaiteki/lib/ui/shared/posts/compose/attachment_tray_item.dart

@@ -51,6 +51,7 @@ class AttachmentTrayItem extends StatelessWidget {
           );
           break;
         }
+      default:
     }
 
     return Padding(

src/kaiteki/lib/ui/shared/posts/compose/compose_form.dart

@@ -299,6 +299,8 @@ class ComposeFormState extends ConsumerState<ComposeForm> {
         } else {
           return PostWidget(snapshot.data!, showActions: false);
         }
+
+      default:
     }
 
     return const Padding(