feat(tui): render LaTeX in markdown

[rumpl]

Summary

• add a dependency-free LaTeX-to-Unicode terminal renderer
• render inline and display math in TUI Markdown
• preserve unsupported, incomplete, currency, shell-variable, and code content
• cover renderer output with golden tests and Markdown integration tests

Validation

• task format
• task test (with MOONSHOT_API_KEY unset to skip the opt-in live API test)
• task lint
• task build

[docker-agent]

Assessment: 🟡 NEEDS ATTENTION

One NOTABLE finding (medium severity, LIKELY confirmed) was identified in the new inline LaTeX rendering code.