feat: enhance user interface with improved styling and responsiveness

- Updated UserAvatar component to accept additional className for better customization.
- Refined ProfilePage layout with responsive avatar styling.
- Enhanced Header component with improved background and text styles.
- Improved PopularTags and TopFriends components with better spacing and text shadows.
- Updated ThoughtCard and ThoughtThread components for better visual hierarchy and responsiveness.
- Enhanced UI components (Button, Badge, Card, DropdownMenu, Input, Popover, Separator, Skeleton, Textarea) with new styles and effects.
- Added a new background image for visual enhancement.

thoughts-frontend/components/ui/skeleton.tsx

@@ -1,13 +1,13 @@
-import { cn } from "@/lib/utils"
+import { cn } from "@/lib/utils";
 
 function Skeleton({ className, ...props }: React.ComponentProps<"div">) {
   return (
     <div
       data-slot="skeleton"
-      className={cn("bg-accent animate-pulse rounded-md", className)}
+      className={cn("bg-muted/50 animate-pulse rounded-md", className)}
       {...props}
     />
-  )
+  );
 }
 
-export { Skeleton }
+export { Skeleton };