feat: implement payment proxy routes and add security validation tests for wallet and intent operations

frontend/app/api/payments/reconcile-latest/route.ts

@@ -2,7 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import {
   applyAuthResponseCookies,
   buildBackendRequestHeaders,
-  requireBackendAuthUser,
+  requireBackendPaymentAuth,
 } from "@/lib/backend-auth";
 import { buildProxyExceptionResponse } from "@/lib/api-proxy";
 
@@ -18,7 +18,7 @@ export async function POST(req: NextRequest) {
 
   try {
     const auth = await buildBackendRequestHeaders(req);
-    const authError = requireBackendAuthUser(auth);
+    const authError = requireBackendPaymentAuth(auth);
     if (authError) return authError;
     const res = await fetch(`${API_BASE}/api/payments/reconcile-latest`, {
       method: "POST",