fix(print): escape markup in echoed stdin prompts

[lihailong00]

Summary

• render stdin prompts literally instead of interpreting user text as Rich markup
• keep the prompt passed to the model byte-for-byte unchanged
• cover normal and markup-like stdin input

Reproduction and verification

Before the fix, the issue example containing [/login] deterministically raised rich.errors.MarkupError. After the fix:

• uv run pytest tests/ui_and_conv/test_print_exit_code.py -q — 25 passed
• targeted Ruff and Pyright — passed

Closes #1291

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.