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/db/migrations/020_purchase_intentions_custom_offer.sql

@@ -0,0 +1,17 @@
+-- Migration 020: Custom offer fields for purchase intentions
+-- Criado em: 2025-02-07
+
+ALTER TABLE purchase_intentions
+  ADD COLUMN IF NOT EXISTS custom_offer_amount NUMERIC(12, 2),
+  ADD COLUMN IF NOT EXISTS custom_offer_currency VARCHAR(20),
+  ADD COLUMN IF NOT EXISTS custom_offer_created_at TIMESTAMP WITHOUT TIME ZONE;
+
+-- Atualizar registros existentes para evitar valores inconsistentes
+UPDATE purchase_intentions
+SET custom_offer_amount = NULL,
+    custom_offer_currency = NULL,
+    custom_offer_created_at = NULL
+WHERE custom_offer_amount IS NOT NULL
+  OR custom_offer_currency IS NOT NULL
+  OR custom_offer_created_at IS NOT NULL;
+