feat: Add JWT authentication to backend, configure frontend API client, fix streak layout

src/app/admin/coupons/page.tsx

@@ -1,5 +1,6 @@
 "use client"
 
+import { fetchWithAuth } from "@/lib/apiClient";
 import { useState, useEffect } from "react"
 import { Card, CardContent, CardHeader, CardTitle, CardDescription } from "@/components/ui/card"
 import { Button } from "@/components/ui/button"
@@ -25,7 +26,7 @@ export default function CouponsAdmin() {
 
   const fetchCoupons = async () => {
     try {
-      const res = await fetch('/api/admin/coupons')
+      const res = await fetchWithAuth('/api/admin/coupons')
       const data = await res.json()
       setCoupons(data)
     } catch (e) {
@@ -39,7 +40,7 @@ export default function CouponsAdmin() {
     if (!newCoupon.code) return
     setSubmitting(true)
     try {
-      await fetch('/api/admin/coupons', {
+      await fetchWithAuth('/api/admin/coupons', {
         method: "POST",
         headers: { "Content-Type": "application/json" },
         body: JSON.stringify(newCoupon)
@@ -56,7 +57,7 @@ export default function CouponsAdmin() {
   const handleDelete = async (id: string) => {
     if (!confirm("Delete this coupon?")) return
     try {
-      await fetch(`/api/admin/coupons/${id}`, { method: "DELETE" })
+      await fetchWithAuth(`/api/admin/coupons/${id}`, { method: "DELETE" })
       await fetchCoupons()
     } catch (e) {
       console.error(e)