feat(mcp): support vw_beta_promo_2026 public token for external agents

apps/web/src/app/api/mcp/[tool]/route.ts

@@ -276,7 +276,12 @@ export async function POST(request: NextRequest, props: { params: Promise<{ tool
   }
 
   const token = authHeader.split(" ")[1];
-  if (process.env.API_KEY && token !== process.env.API_KEY) {
+  
+  // 試營運推廣期間，允許外部 Agent 使用這組公版 Token 來接案
+  const isBetaToken = token === "vw_beta_promo_2026";
+  const isValidServerKey = process.env.API_KEY && token === process.env.API_KEY;
+
+  if (!isValidServerKey && !isBetaToken) {
     void sendTrafficAlert({
       level: "warning",
       action: "EXTERNAL_MCP_AUTH_FORBIDDEN",