style(workout-session-header.tsx): update background styles for cards to enhance visual consistency and improve dark mode support

src/features/workout-session/ui/workout-session-header.tsx

@@ -75,7 +75,7 @@ export function WorkoutSessionHeader({
 
           <div className="grid grid-cols-1 sm:grid-cols-3 gap-3">
             {/* Card 1: elapsed time */}
-            <div className="bg-white dark:bg-gradient-to-br dark:from-slate-800/80 dark:to-slate-700/80 rounded-lg p-3 border border-slate-200 dark:border-slate-600/30">
+            <div className="bg-white dark:bg-slate-800 rounded-lg p-3 border border-slate-200 dark:border-slate-700 transition-colors duration-200 dark:text-white dark:hover:bg-slate-700">
               <div className="flex items-center gap-2 mb-2">
                 <div className="w-8 h-8 rounded-full bg-blue-500/20 flex items-center justify-center">
                   <Clock className="h-4 w-4 text-blue-400" />
@@ -113,7 +113,7 @@ export function WorkoutSessionHeader({
             </div>
 
             {/* Card 2: progress */}
-            <div className="bg-white dark:bg-gradient-to-br dark:from-slate-800/80 dark:to-slate-700/80 rounded-lg p-3 border border-slate-200 dark:border-slate-600/30">
+            <div className="bg-white dark:bg-slate-800 rounded-lg p-3 border border-slate-200 dark:border-slate-700 transition-colors duration-200 dark:text-white dark:hover:bg-slate-700">
               <div className="flex items-center gap-2 mb-2">
                 <div className="w-8 h-8 rounded-full bg-purple-500/20 flex items-center justify-center">
                   <Target className="h-4 w-4 text-purple-400" />