공부 타이머 통계 박스 오버플로우 수정

초단위까지 표시하면서 "50시간 57분 0초"처럼 길어진 값이 줄바꿈되며
박스 밖으로 넘치던 문제를, FittedBox로 한 줄에 맞게 자동 축소되도록 수정.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/ui/study_timer_screen.dart

@@ -507,20 +507,25 @@ class _StudyTimerScreenState extends State<StudyTimerScreen>
 
   Widget _statBox(String label, String value) {
     return Container(
-      width: 100,
-      padding: const EdgeInsets.symmetric(vertical: 14),
+      width: 108,
+      padding: const EdgeInsets.symmetric(vertical: 14, horizontal: 6),
       decoration: BoxDecoration(
         color: AppPalette.paper,
         borderRadius: BorderRadius.circular(16),
         border: Border.all(color: AppPalette.sage),
       ),
       child: Column(
+        mainAxisSize: MainAxisSize.min,
         children: [
           Text(label, style: TextStyle(color: Colors.grey[600], fontSize: 12)),
           const SizedBox(height: 4),
-          Text(
-            value,
-            style: const TextStyle(fontWeight: FontWeight.bold, fontSize: 15),
+          FittedBox(
+            fit: BoxFit.scaleDown,
+            child: Text(
+              value,
+              maxLines: 1,
+              style: const TextStyle(fontWeight: FontWeight.bold, fontSize: 15),
+            ),
           ),
         ],
       ),