[Fix] Telegram Fast replies show a blank draft before streaming

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote, in the web UI, or in Telegram.

What changed

• Start private-chat Fast turns with a non-empty Roomote is working... native Telegram draft instead of an empty draft, matching Slack's rendered copy.
• Replace that placeholder under the same nonzero draft ID with the first model partial, retaining immediate first-chunk delivery and paced later updates.
• Add deterministic coverage for the exact working-status copy, no empty draft writes, stable topic-scoped draft identity, refresh behavior, fallback, and final delivery; update the Telegram guide to match.

Why this change was made

Telegram documents empty draft text as a native Thinking placeholder, but some clients render that state as a blank draft. A literal non-empty placeholder avoids the client-dependent empty rendering while using Telegram's documented same-ID animated draft updates for streamed text.

Official contracts: sendMessageDraft and sendChatAction.

Impact

Private chats and private topics show the same Roomote is working... pre-output copy as Slack and then show incremental response text without a blank draft. Group typing fallback, provider credential isolation, draft failure fallback, and durable final-message delivery are unchanged.

[roomote-community]

No new code issues found. See task

_{Reviewed cc582ca}