feat(tgapp): stream MarkdownV2 replies with draft fallback and file segments

[YooooEX]

Context

Telegram currently streams replies through a polling + HTML path, which makes draft updates, MarkdownV2 rendering, long-message splitting, and attachment delivery inconsistent with the newer chat frontend behavior.
This PR keeps the change radius inside frontends/tgapp.py plus focused regression tests. No new dependencies are added.

Summary

Upgrade Telegram reply streaming to use MarkdownV2-first draft/live updates, segmented final output, and attachment-aware delivery.

Changes

frontends/tgapp.py

• switch Telegram streaming from fixed-interval polling edits to event-driven queue consumption
• prefer reply_text_draft(...) in private chats and fall back to normal reply/edit flows when draft updates are unavailable
• render replies with MarkdownV2 escaping instead of the previous HTML conversion path
• split long final replies into multiple visible segments instead of truncating or restarting from the tail
• strip [FILE:...] hints from visible text and send extracted files as Telegram attachments after finalize
• keep stop/error flows explicit by finalizing the current stream session with a notice

[lsdefine]

LGTM