Enhance Documentation: Added JSDoc to getRequestId Function

lib/request-id.ts

@@ -1,5 +1,16 @@
 import { headers } from 'next/headers';
-
+/**
+ * Retrieves the `x-request-id` header value from the current incoming server request.
+ * This header is typically set by the hosting platform (e.g., Vercel) or an upstream
+ * proxy to enable request tracing and log correlation.
+ *
+ * @returns The request ID string if present, or null if the header is absent.
+ * @example
+ * ```ts
+ * const requestId = await getRequestId();
+ * console.log(requestId); // "req_abc123xyz"
+ * ```
+ */
 export async function getRequestId() {
   const h = await headers();
   return h.get('x-request-id');