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/textarea.tsx

@@ -0,0 +1,22 @@
+import * as React from "react"
+
+import { cn } from "@/lib/utils"
+
+const Textarea = React.forwardRef<
+  HTMLTextAreaElement,
+  React.ComponentProps<"textarea">
+>(({ className, ...props }, ref) => {
+  return (
+    <textarea
+      className={cn(
+        "flex min-h-[60px] w-full rounded-md border border-input bg-transparent px-3 py-2 text-base shadow-sm placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring disabled:cursor-not-allowed disabled:opacity-50 md:text-sm",
+        className
+      )}
+      ref={ref}
+      {...props}
+    />
+  )
+})
+Textarea.displayName = "Textarea"
+
+export { Textarea }