feat: enhance frontend with new UI components and Tailwind CSS integration

- Added CreateButton and DocumentCard components for document management.
- Implemented tabbed interface for owned and shared documents in Home page.
- Integrated Tailwind CSS for styling and layout improvements.
- Introduced utility functions for class name management.
- Updated package.json with new dependencies for UI components and styling.
- Created PostCSS configuration for Tailwind CSS.
- Refactored Navbar and button components for better usability and design.
- Enhanced document API to include owner_id for document sharing functionality.

frontend/@/components/ui/tabs.tsx

@@ -0,0 +1,53 @@
+import * as React from "react"
+import * as TabsPrimitive from "@radix-ui/react-tabs"
+
+import { cn } from "@/lib/utils"
+
+const Tabs = TabsPrimitive.Root
+
+const TabsList = React.forwardRef<
+  React.ElementRef<typeof TabsPrimitive.List>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.List>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.List
+    ref={ref}
+    className={cn(
+      "inline-flex h-10 items-center justify-center rounded-md bg-muted p-1 text-muted-foreground",
+      className
+    )}
+    {...props}
+  />
+))
+TabsList.displayName = TabsPrimitive.List.displayName
+
+const TabsTrigger = React.forwardRef<
+  React.ElementRef<typeof TabsPrimitive.Trigger>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.Trigger>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.Trigger
+    ref={ref}
+    className={cn(
+      "inline-flex items-center justify-center whitespace-nowrap rounded-sm px-3 py-1.5 text-sm font-medium ring-offset-background transition-all focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 disabled:pointer-events-none disabled:opacity-50 data-[state=active]:bg-background data-[state=active]:text-foreground data-[state=active]:shadow-sm",
+      className
+    )}
+    {...props}
+  />
+))
+TabsTrigger.displayName = TabsPrimitive.Trigger.displayName
+
+const TabsContent = React.forwardRef<
+  React.ElementRef<typeof TabsPrimitive.Content>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.Content>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.Content
+    ref={ref}
+    className={cn(
+      "mt-2 ring-offset-background focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2",
+      className
+    )}
+    {...props}
+  />
+))
+TabsContent.displayName = TabsPrimitive.Content.displayName
+
+export { Tabs, TabsList, TabsTrigger, TabsContent }