feat(inventory): add API routes for GET and POST inventory

frontend/app/api/inventory/route.ts

@@ -0,0 +1,34 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getAuthHeaders } from '../../../lib/auth-headers';
+
+const API_BASE =
+  process.env.NEXT_PUBLIC_API_URL_INTERNAL || 'http://recipe-api:8080';
+
+export async function GET(request: NextRequest) {
+  const authHeaders = await getAuthHeaders();
+  const search = request.nextUrl.search;
+  const res = await fetch(`${API_BASE}/api/inventory${search}`, {
+    headers: { ...authHeaders },
+    cache: 'no-store',
+  });
+  const text = await res.text();
+  return new NextResponse(text, {
+    status: res.status,
+    headers: { 'Content-Type': 'application/json' },
+  });
+}
+
+export async function POST(request: NextRequest) {
+  const authHeaders = await getAuthHeaders();
+  const body = await request.json();
+  const res = await fetch(`${API_BASE}/api/inventory`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json', ...authHeaders },
+    body: JSON.stringify(body),
+  });
+  const text = await res.text();
+  return new NextResponse(text, {
+    status: res.status,
+    headers: { 'Content-Type': 'application/json' },
+  });
+}