fix(migration): add deduplication step before creating index

prisma/postgresql-migrations/20251122003044_add_chat_instance_remotejid_unique/migration.sql

@@ -1,2 +1,16 @@
--- AlterTable
+-- 1. Cleanup: Remove duplicate chats, keeping the most recently updated one
+DELETE FROM "Chat"
+WHERE id IN (
+  SELECT id FROM (
+    SELECT id,
+           ROW_NUMBER() OVER (
+             PARTITION BY "instanceId", "remoteJid"
+             ORDER BY "updatedAt" DESC
+           ) as row_num
+    FROM "Chat"
+  ) t
+  WHERE t.row_num > 1
+);
+
+-- 2. Create the unique index (Constraint)
 CREATE UNIQUE INDEX "Chat_instanceId_remoteJid_key" ON "Chat"("instanceId", "remoteJid");