Support Telegram forum topics

[thebiglabasky]

Summary

• add optional messageThreadId support to TelegramAlertChannel
• serialize it as Telegram's message_thread_id request parameter
• preserve the value when exporting existing Telegram alert channels to code
• retain the existing template shape when no topic is configured

Why

This closes the CLI round-trip gap in ENG-22. Without this change, exporting a topic-enabled channel and redeploying it would silently remove its topic routing.

Validation

• focused construct and codegen tests — 3 tests passed
• ESLint on all touched files
• pnpm --dir packages/cli pack
• git diff --check

[thebiglabasky]

CI note: the Telegram-focused construct/codegen tests, lint, and package build pass. The remaining CLI failure is the pre-existing global retry-project e2e in e2e/__tests__/test.spec.ts:312: it expects four “Failing Check Result” lines but receives one. It failed identically on Ubuntu and Windows shard 3/4, and the isolated Ubuntu rerun reproduced it. None of this PR's four changed files touch that test or retry execution. I have left this PR scoped to ENG-22 rather than folding an unrelated retry regression into it.