feat: add new dashboard components and enhance UI

- Introduced new CSS variables for light theme in `globals.css` to improve visual consistency.
- Replaced `Card` component with `StatCard`, `ProgressBar`, and `MetricCard` in `DashboardStats`, `ProductivityAnalytics`, and `RecentTasks` for better modularity and reusability.
- Updated `QuickActions` to use `ActionCard` for a more cohesive design.
- Enhanced `Badge` and `Button` components with new variants for improved styling options.
- Added new UI showcase section in `UIShowcaseClient` to demonstrate the new dashboard components.

src/app/globals.css

@@ -24,6 +24,30 @@
   --gray-light: #e5e7eb; /* gray-200 */
 }
 
+.light {
+  /* Light theme explicit */
+  --background: #f1f5f9; /* slate-100 */
+  --foreground: #0f172a; /* slate-900 */
+  --card: #ffffff; /* white */
+  --card-hover: #f8fafc; /* slate-50 */
+  --card-column: #f8fafc; /* slate-50 */
+  --border: #cbd5e1; /* slate-300 */
+  --input: #ffffff; /* white */
+  --primary: #0891b2; /* cyan-600 */
+  --primary-foreground: #ffffff; /* white */
+  --muted: #94a3b8; /* slate-400 */
+  --muted-foreground: #64748b; /* slate-500 */
+  --accent: #d97706; /* amber-600 */
+  --destructive: #dc2626; /* red-600 */
+  --success: #059669; /* emerald-600 */
+  --purple: #8b5cf6; /* purple-500 */
+  --yellow: #eab308; /* yellow-500 */
+  --green: #059669; /* emerald-600 */
+  --blue: #2563eb; /* blue-600 */
+  --gray: #6b7280; /* gray-500 */
+  --gray-light: #e5e7eb; /* gray-200 */
+}
+
 .dark {
   /* Dark theme override */
   --background: #1e293b; /* slate-800 - encore plus clair */