feat: apply markdown rendering to HITL email, sanitize email subject and body (#32305)

This PR:

1. Fixes the bug that email body of `HumanInput` node are sent as-is, without markdown rendering or sanitization
2. Applies HTML sanitization to email subject and body
3. Removes `\r` and `\n` from email subject to prevent SMTP header injection

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: QuantumGhost <[email protected]>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>