Feature: Support Telegram Topics/Forum threads in DMs and Groups

Problem

When a Telegram bot has Topics enabled (via BotFather), messages from topic threads don't include message_thread_id in the agent's message envelope. This means:

• Agent can't tell which topic a message came from
• Agent can't route replies back to the correct topic (they land in General)

Current behavior

• Inbound messages show only message_id, no thread context
• message tool accepts threadId param but agent has no way to know what value to use

Expected behavior

1. Inbound envelope should include threadId or message_thread_id when present
2. Replies should auto-target the originating thread (like replyToMode does for message replies)

Context

• Works for both DM-with-Topics and Group Forums
• BotFather setting: "Topics in Groups" / bot added to forum-enabled group or DM
• Telegram API provides message_thread_id in updates

Suggested implementation

1. Parse message_thread_id from Telegram Update
2. Add to envelope metadata (e.g., [threadId: 123])
3. Store in session context for reply routing
4. Use for outbound sendMessage calls automatically