Add foundational API client, UI components, and state management setup

- Created `generate-api-client.sh` for OpenAPI-based TypeScript client generation.
- Added `src/lib/api` with Axios-based API client, error handling utilities, and placeholder for generated types.
- Implemented Zustand-based `authStore` for user authentication and token management.
- Integrated reusable UI components (e.g., `Dialog`, `Select`, `Textarea`, `Sheet`, `Separator`, `Checkbox`) using Radix UI and utility functions.
- Established groundwork for client-server integration, state management, and modular UI development.

frontend/src/components/ui/avatar.tsx

@@ -0,0 +1,50 @@
+"use client"
+
+import * as React from "react"
+import * as AvatarPrimitive from "@radix-ui/react-avatar"
+
+import { cn } from "@/lib/utils"
+
+const Avatar = React.forwardRef<
+  React.ElementRef<typeof AvatarPrimitive.Root>,
+  React.ComponentPropsWithoutRef<typeof AvatarPrimitive.Root>
+>(({ className, ...props }, ref) => (
+  <AvatarPrimitive.Root
+    ref={ref}
+    className={cn(
+      "relative flex h-10 w-10 shrink-0 overflow-hidden rounded-full",
+      className
+    )}
+    {...props}
+  />
+))
+Avatar.displayName = AvatarPrimitive.Root.displayName
+
+const AvatarImage = React.forwardRef<
+  React.ElementRef<typeof AvatarPrimitive.Image>,
+  React.ComponentPropsWithoutRef<typeof AvatarPrimitive.Image>
+>(({ className, ...props }, ref) => (
+  <AvatarPrimitive.Image
+    ref={ref}
+    className={cn("aspect-square h-full w-full", className)}
+    {...props}
+  />
+))
+AvatarImage.displayName = AvatarPrimitive.Image.displayName
+
+const AvatarFallback = React.forwardRef<
+  React.ElementRef<typeof AvatarPrimitive.Fallback>,
+  React.ComponentPropsWithoutRef<typeof AvatarPrimitive.Fallback>
+>(({ className, ...props }, ref) => (
+  <AvatarPrimitive.Fallback
+    ref={ref}
+    className={cn(
+      "flex h-full w-full items-center justify-center rounded-full bg-muted",
+      className
+    )}
+    {...props}
+  />
+))
+AvatarFallback.displayName = AvatarPrimitive.Fallback.displayName
+
+export { Avatar, AvatarImage, AvatarFallback }