feat: enhance purchase intentions with chat integration and offer tracking

- Added MongoDB chat/message integration for seller responses
- Improved seller response validation and default messaging
- Integrated automatic chat creation/update when responding to intentions
- Added highest custom offer fields to listing queries and models
- Enhanced listing data with top offer information for buyers

lib/auth/middleware.ts

@@ -31,6 +31,8 @@ function extractToken(request: NextRequest): string | null {
 }
 
 /**
+ * Converte payload de token em objeto AuthenticatedUser.
+ */
 function toAuthenticatedUser(payload: {
   userId: number;
   username: string;