feat: add reply/quoted message context support

Add generic reply context fields to NewMessage (reply_to_message_id,
reply_to_message_content, reply_to_sender_name) so any channel can
pass quoted message context to the agent.

- Add thread_id and reply_to_* fields to NewMessage interface
- Add DB migration for reply context columns on messages table
- Update storeMessage/getMessagesSince/getNewMessages to persist and
  retrieve reply fields
- Render reply context as <quoted_message> XML in formatMessages
- Add DB and formatting tests

Co-Authored-By: Alfred-the-buttler <leon.alfred.bot@gmail.com>
Co-Authored-By: moktamd <moktamd@users.noreply.github.com>
Co-Authored-By: gurixs-carson <gurixs-carson@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/types.ts

@@ -51,6 +51,10 @@ export interface NewMessage {
   timestamp: string;
   is_from_me?: boolean;
   is_bot_message?: boolean;
+  thread_id?: string;
+  reply_to_message_id?: string;
+  reply_to_message_content?: string;
+  reply_to_sender_name?: string;
 }
 
 export interface ScheduledTask {