Telegram thread/topic replies lose thread context

[Davidsod]

Problem

When a message arrives in a Telegram thread (forum topic), the thread_id is captured by the Telegram channel (src/channels/telegram.ts:158,226) and TelegramChannel.sendMessage() supports a threadId parameter (line 368). However, the reply is sent without thread context because:

1. thread_id is not persisted in the messages table — src/db.ts has no thread_id column
2. Callers never pass threadId — src/index.ts:297, :712, :719 all call channel.sendMessage(jid, text) without it
3. The Channel interface in src/types.ts defines sendMessage(jid: string, text: string) without a threadId parameter (even though TelegramChannel accepts one as an optional third arg)

Result

Bot replies land in the main chat instead of the thread/topic where the user sent the message.

Suggested Fix

1. Add thread_id TEXT column to the messages table in src/db.ts
2. Store thread_id when inserting messages (it's already on the NewMessage type at src/types.ts:54)
3. When sending a reply, look up the most recent thread_id for the chat JID and pass it through
4. Update Channel.sendMessage signature to accept an optional threadId
5. Update all sendMessage call sites in src/index.ts to pass the thread context

This affects the core message flow, so it should be fixed upstream rather than patched locally.