style(mobile): 일정 상세 액션바 카테고리 텍스트 font-bold로 변경

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/mobile/schedule/ScheduleDetail.jsx

@@ -743,7 +743,7 @@ function MobileScheduleDetail() {
       {/* 헤더 */}
       <div className="flex-shrink-0 bg-white border-b border-gray-100">
         <div className="flex items-center justify-center h-14 px-4">
-          <span className="text-sm font-medium" style={{ color: schedule.category?.color }}>
+          <span className="text-base font-bold" style={{ color: schedule.category?.color }}>
             {schedule.category?.name}
           </span>
         </div>