feat: update Card components to use variant="glass"

- Changed Card components in various charts and dashboard sections to use the "glass" variant for a consistent UI enhancement.
- This update affects CompletionTrendChart, PriorityDistributionChart, VelocityChart, WeeklyStatsCard, DashboardStats, ProductivityAnalytics, RecentTasks, TagDistributionChart, MetricsDistributionCharts, MetricsMainCharts, CriticalDeadlinesCard, DeadlineRiskCard, DeadlineSummaryCard, and StatCard.

src/components/deadline/CriticalDeadlinesCard.tsx

@@ -53,7 +53,7 @@ export function CriticalDeadlinesCard({ overdue, critical, warning, disableHover
 
   if (urgentTasks.length === 0) {
     return (
-      <Card className="p-6 hover:shadow-lg transition-shadow">
+      <Card variant="glass" className="p-6 hover:shadow-lg transition-shadow">
         <h3 className="text-lg font-semibold mb-4">Tâches Urgentes</h3>
         <div className="text-center py-8">
           <div className="text-4xl mb-2">🎉</div>
@@ -67,7 +67,7 @@ export function CriticalDeadlinesCard({ overdue, critical, warning, disableHover
   }
 
   return (
-    <Card className="p-6 hover:shadow-lg transition-shadow">
+    <Card variant="glass" className="p-6 hover:shadow-lg transition-shadow">
       <div className="flex items-center justify-between mb-4">
         <h3 className="text-lg font-semibold">Tâches Urgentes</h3>
         <div className="text-sm text-[var(--muted-foreground)]">