fix(telegram): render markdown messages safely

[cyq1017]

Refs #2967

Problem

Telegram bridge replies currently send raw Markdown-looking text, so code, links, and simple tables render poorly on phones. Enabling MarkdownV2 directly is risky because Telegram parse errors can drop the message.

Change

• Render Telegram messages as MarkdownV2 with escaping for text, links, inline code, fenced code, and simple pipe tables.
• Fall back to stripped plain text when MarkdownV2 would exceed the chunk limit or Telegram returns a parse error.
• Keep existing chunking, retry, and reply markup behavior.

Verification

• npm test
• npm run check
• git diff --check upstream/main...HEAD