feat(API-11): Route API calls through AgilitonAPI gateway

Add gateway-first pattern: when AGILITON_API_KEY is set, route all
external API calls through the gateway with X-API-Key auth. Falls back
to direct API access when gateway is unavailable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

node_modules/@hono/node-server/dist/vercel.d.mts

@@ -0,0 +1,7 @@
+import * as http2 from 'http2';
+import * as http from 'http';
+import { Hono } from 'hono';
+
+declare const handle: (app: Hono<any, any, any>) => (incoming: http.IncomingMessage | http2.Http2ServerRequest, outgoing: http.ServerResponse | http2.Http2ServerResponse) => Promise<void>;
+
+export { handle };