fix(telegram): preserve DM topic threadId in deliveryContext

When receiving messages in Telegram DM topics (Topics in Private Chats),
the threadId was not saved in the session's deliveryContext, causing
replies to go to General chat instead of the topic.

Now we pass threadId to updateLastRoute for DM topics.

Fixes #8891

src/telegram/bot-message-context.ts

@@ -637,6 +637,8 @@ export const buildTelegramMessageContext = async ({
           channel: "telegram",
           to: String(chatId),
           accountId: route.accountId,
+          // Preserve DM topic threadId for replies (fixes #8891)
+          threadId: dmThreadId != null ? String(dmThreadId) : undefined,
         }
       : undefined,
     onRecordError: (err) => {