refactor(app): 앱 설정 및 공유 위젯 업데이트

- app.dart: MaterialApp 설정 개선
- retro_panel: 레트로 패널 위젯 수정

lib/src/shared/widgets/retro_panel.dart

@@ -14,7 +14,11 @@ class RetroPanel extends StatelessWidget {
     this.borderWidth = 3.0,
     this.useGoldBorder = false,
     this.title,
-  });
+    this.titleWidget,
+  }) : assert(
+         title == null || titleWidget == null,
+         'title과 titleWidget 중 하나만 사용 가능',
+       );
 
   /// 패널 내부 컨텐츠
   final Widget child;
@@ -34,6 +38,9 @@ class RetroPanel extends StatelessWidget {
   /// 패널 타이틀 (상단에 표시)
   final String? title;
 
+  /// 커스텀 타이틀 위젯 (title 대신 사용)
+  final Widget? titleWidget;
+
   @override
   Widget build(BuildContext context) {
     final painter = useGoldBorder
@@ -46,16 +53,24 @@ class RetroPanel extends StatelessWidget {
             fillColor: backgroundColor,
           );
 
+    final hasTitle = title != null || titleWidget != null;
+
     return CustomPaint(
       painter: painter,
       child: Padding(
         padding: EdgeInsets.all(borderWidth).add(padding),
-        child: title != null
+        child: hasTitle
             ? Column(
                 crossAxisAlignment: CrossAxisAlignment.stretch,
                 mainAxisSize: MainAxisSize.min,
                 children: [
-                  _PanelTitle(title: title!, useGoldBorder: useGoldBorder),
+                  if (titleWidget != null)
+                    _PanelTitleContainer(
+                      useGoldBorder: useGoldBorder,
+                      child: titleWidget!,
+                    )
+                  else
+                    _PanelTitle(title: title!, useGoldBorder: useGoldBorder),
                   const SizedBox(height: 8),
                   Flexible(child: child),
                 ],
@@ -73,6 +88,33 @@ class _PanelTitle extends StatelessWidget {
   final String title;
   final bool useGoldBorder;
 
+  @override
+  Widget build(BuildContext context) {
+    return _PanelTitleContainer(
+      useGoldBorder: useGoldBorder,
+      child: Text(
+        title.toUpperCase(),
+        style: TextStyle(
+          fontFamily: 'PressStart2P',
+          fontSize: 14,
+          color: useGoldBorder ? RetroColors.gold : RetroColors.textLight,
+          letterSpacing: 1,
+        ),
+      ),
+    );
+  }
+}
+
+/// 패널 타이틀 컨테이너 (커스텀 위젯용)
+class _PanelTitleContainer extends StatelessWidget {
+  const _PanelTitleContainer({
+    required this.useGoldBorder,
+    required this.child,
+  });
+
+  final bool useGoldBorder;
+  final Widget child;
+
   @override
   Widget build(BuildContext context) {
     return Container(
@@ -90,15 +132,7 @@ class _PanelTitle extends StatelessWidget {
           ),
         ),
       ),
-      child: Text(
-        title.toUpperCase(),
-        style: TextStyle(
-          fontFamily: 'PressStart2P',
-          fontSize: 14,
-          color: useGoldBorder ? RetroColors.gold : RetroColors.textLight,
-          letterSpacing: 1,
-        ),
-      ),
+      child: child,
     );
   }
 }
@@ -110,11 +144,16 @@ class RetroGoldPanel extends StatelessWidget {
     required this.child,
     this.padding = const EdgeInsets.all(12),
     this.title,
-  });
+    this.titleWidget,
+  }) : assert(
+         title == null || titleWidget == null,
+         'title과 titleWidget 중 하나만 사용 가능',
+       );
 
   final Widget child;
   final EdgeInsets padding;
   final String? title;
+  final Widget? titleWidget;
 
   @override
   Widget build(BuildContext context) {
@@ -122,6 +161,7 @@ class RetroGoldPanel extends StatelessWidget {
       useGoldBorder: true,
       padding: padding,
       title: title,
+      titleWidget: titleWidget,
       child: child,
     );
   }