feat: implement user authentication and admin management

- Add user management API endpoints for listing and creating users.
- Implement login and logout functionality with rate limiting.
- Create UI components for login form, logout button, and animated elements.
- Add session management with JWT and secure cookie handling.
- Seed initial admin user if no users exist.
- Introduce utility functions for password hashing and user authentication.
- Set up proxy middleware for route protection and security headers.
- Create a JSON file for user data storage.
- Add links configuration for external resources.

frontend/app/api/upload/route.ts

@@ -1,12 +1,18 @@
 import { NextResponse } from 'next/server'
 import { nanoid } from 'nanoid'
 import { addFile } from '@/lib/store'
+import { getSession } from '@/lib/session'
 import type { FileRecord } from '@/lib/store'
 
 const ALLOWED_EXTENSIONS = ['.backerup', '.json']
 const MAX_SIZE_BYTES = 500 * 1024 * 1024 // 500 MB
 
 export async function POST(request: Request) {
+  // Belt-and-suspenders auth check (middleware handles the primary check)
+  const session = await getSession()
+  if (!session) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+  }
   let formData: FormData
   try {
     formData = await request.formData()