chore(lint): prefer-const for billTo in ask-ai route

app/api/ask-ai/route.ts

@@ -71,7 +71,7 @@ export async function POST(request: NextRequest) {
   // Optional: allow billing to a specific org if the token has permissions.
   // If not set, we bill to the token owner (recommended for demo tokens).
   const BILL_TO_ORG = process.env.BILL_TO_ORG;
-  let billTo: string | null = BILL_TO_ORG ?? null;
+  const billTo: string | null = BILL_TO_ORG ?? null;
 
   /**
    * Handle local usage token, this bypass the need for a user token
@@ -254,7 +254,7 @@ export async function PUT(request: NextRequest) {
 
   let token = userToken;
   const BILL_TO_ORG = process.env.BILL_TO_ORG;
-  let billTo: string | null = BILL_TO_ORG ?? null;
+  const billTo: string | null = BILL_TO_ORG ?? null;
 
   /**
    * Handle local usage token, this bypass the need for a user token