feat: implement new layout components and routing structure

- Added HeaderLayout component for the application header.
- Introduced KeepAliveViewport for managing tab states and rendering.
- Created TabNav for tab navigation with animated indicator.
- Removed old Tabs component in favor of new layout structure.
- Updated routing with AppRouter and defined appTabs for navigation.
- Enhanced theme context to manage dark mode styles.
- Added new UI components: Badge, Button, Separator, and Tabs.
- Refactored pages to utilize new layout components and improve responsiveness.
- Updated global styles for better theming and layout consistency.
- Introduced TypeScript path aliases for cleaner imports.

frontend/src/components/shadcn/ui/badge.tsx

@@ -0,0 +1,30 @@
+import { cva, type VariantProps } from 'class-variance-authority';
+import type * as React from 'react';
+
+import { cn } from '@/lib/utils';
+
+const badgeVariants = cva(
+  'inline-flex items-center rounded-md border px-2 py-1 text-[11px] font-medium tracking-[0.22em] uppercase transition-colors',
+  {
+    variants: {
+      variant: {
+        default: 'border-primary/30 bg-primary/10 text-primary',
+        secondary: 'border-border bg-muted text-muted-foreground',
+        outline: 'border-border bg-transparent text-foreground',
+      },
+    },
+    defaultVariants: {
+      variant: 'default',
+    },
+  },
+);
+
+function Badge({
+  className,
+  variant,
+  ...props
+}: React.ComponentProps<'span'> & VariantProps<typeof badgeVariants>) {
+  return <span className={cn(badgeVariants({ variant }), className)} {...props} />;
+}
+
+export { Badge };