ci: enforce flutter/biome format checks and fix front lint violations

userfront/lib/core/widgets/language_selector.dart

@@ -15,10 +15,7 @@ class LanguageSelector extends StatelessWidget {
   Widget build(BuildContext context) {
     final current = context.locale.languageCode;
     final items = [
-      DropdownMenuItem(
-        value: 'ko',
-        child: Text(tr('ui.common.language_ko')),
-      ),
+      DropdownMenuItem(value: 'ko', child: Text(tr('ui.common.language_ko'))),
       DropdownMenuItem(
         value: 'en',
         child: Text(tr('ui.common.language_en', fallback: 'English')),