fix: hybrid default export to satisfy Vercel/Node and Bun/Workers contracts

- Export handler as default function for Vercel Serverless Function runtime.
- Attach fetch method to default export object for Bun and Cloudflare Workers compatibility.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/relay.ts

@@ -280,17 +280,13 @@ async function handleRelay(req: Request): Promise<Response> {
 // ─── Exported Vercel Function Handler ───────────────────────────────────────────
 
 /**
- * Vercel Bun runtime handler.
+ * Hybrid handler for Vercel/Node web-api and Bun/Workers runtimes.
  *
- * Vercel's Bun runtime expects a `default` export that is an object with
- * a `fetch` method — NOT a bare default function.  This matches the
- * standard `Bun.serve()` handler shape.
- *
- * Handles routing, middleware, and relay logic — same semantics as the
- * standalone Bun.serve() server, minus WebSocket support.
+ * Exports both:
+ *   1. Default function: parsed by Vercel Node runtime.
+ *   2. Default.fetch(): parsed by Cloudflare / Bun runtimes.
  */
-export default {
-	async fetch(req: Request): Promise<Response> {
+async function fetchHandler(req: Request): Promise<Response> {
 	const url = new URL(req.url);
 
 	// Static routes — show index only when no relay target is requested
@@ -401,5 +397,8 @@ export default {
 
 	// Generic HTTP relay
 	return handleRelay(req);
-	},
-};
+}
+
+export default Object.assign(fetchHandler, {
+	fetch: fetchHandler,
+});