Add structured chat delivery records

AgentCompany-New/src/main/database/migrations/025-chat-message-delivery.ts

@@ -0,0 +1,10 @@
+export const chatMessageDeliverySchema = `
+  alter table chat_messages add column body_structured_json text not null default '{}';
+  alter table chat_messages add column delivery_state text not null default 'sent';
+
+  create index if not exists idx_chat_messages_delivery_state
+    on chat_messages(org_id, delivery_state, created_at);
+
+  insert into schema_migrations(version, name, applied_at)
+  values (25, 'chat_message_delivery', datetime('now'));
+`;