Add iTerm2 TUI visibility helper

[cbusillo]

Summary

• update the repo-local test-tui skill with precise live/VT100/binary evidence language
• add a skill-bundled macOS/iTerm2 visibility helper using the iTerm2 Python SDK
• use PEP 723 inline script dependencies so agents run it via uv run without creating a venv
• add targeted macOS window screenshot support via Quartz window listing and screencapture -l

Validation

• python3 -m py_compile .codex/skills/test-tui/scripts/iterm2_tui_visibility.py
• uv run .codex/skills/test-tui/scripts/iterm2_tui_visibility.py --help
• uv run .codex/skills/test-tui/scripts/iterm2_tui_visibility.py windows
• uv run .codex/skills/test-tui/scripts/iterm2_tui_visibility.py list returns structured llm_advice because iTerm2's Python API endpoint is not reachable in the current environment
• uv run /Users/cbusillo/Developer/codex-skills/skill-creator/scripts/quick_validate.py .codex/skills/test-tui
• npx prettier --check .codex/skills/test-tui/SKILL.md
• git diff --check
• ./build-fast.sh

Privacy

• no real screenshots, session IDs, window IDs, TTYs, hostnames, or local paths were committed
• runtime captures default under gitignored .code/tui-captures/