fix: escape agent-controlled Rich output

[Rayan-and-beyond]

Summary

• escape agent-controlled descriptions and finding text before Rich renders them
• escape prompt/result content in show while preserving the CLI's own formatting
• add the requested fail-first regression for bracketed descriptions

Closes #29

Validation

• fail-first: focused bracketed-description regression failed before the fix
• PYTHONPATH=. uv run pytest -q tests/test_cli.py -k bracketed_description — 1 passed
• PYTHONPATH=. uv run pytest -q — 52 passed
• uv run ruff check agentrace/cli.py tests/test_cli.py — passed
• git diff --check — passed

The repository-wide Ruff scan still reports pre-existing findings outside these touched lines.

[github-actions]

This is in, @Rayan-and-beyond. Really appreciate it.

Good, focused change. Exactly the kind of thing Agentrace needs.

If Agentrace is useful to you, a star goes a long way.

Happy to see more from you whenever you have the time.