feat(tui): LaTeX math rendering via Unicode substitution

[SparkofSpike]

Summary

Add LaTeX math expression rendering for the TUI transcript. Math delimiters ($...$, ..., (...), [...]) are detected before markdown rendering and converted to Unicode approximations, improving readability of formulas in AI responses.

Changes

• New file: crates/tui/src/tui/history/latex_render.rs (451 lines) — LaTeX-to-Unicode converter with 200+ symbol mappings (Greek, blackboard bold, calligraphic, relations, operators, arrows), superscript/subscript via Unicode combining chars, fractions as (a/b), sqrt, and basic integral/sum/product constructs
• Modify: crates/tui/src/tui/history.rs — Add mod latex_render
• Modify: crates/tui/src/tui/history/message.rs — Three integration points in streaming and full render paths

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change
• Documentation update
• Refactoring (no functional changes)
• Tests

Testing

• cargo fmt
• cargo clippy
• cargo test
• Manual testing — compiled, launched, tested with various formulas

Checklist

• Updated docs or comments as needed
• Added or updated tests where relevant
• Verified TUI behavior manually if UI changes
• Harvested/co-authored credit

Related Issues

Closes #4957

[Hmbown]

Thanks for carrying this through and rebasing it onto current main. I added one maintainer hardening commit on top of your latest head after the local semantic test caught the \\mathbb{R} path: it now preserves Markdown code spans/fences, currency, escaped dollars, and unknown commands, and adds regression coverage. Local cargo fmt, all 9 focused tests, and the exact workspace clippy gate pass. Protected auto-merge is enabled so your contribution and authorship land once the refreshed matrix is green.

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[SparkofSpike]

Oops, so sorry about that — I didn't see your message before force-pushing. Could you please push your commit again? Thanks! @Hmbown

[Hmbown]

I moved the combined work to stable maintainer integration PR #4974 because the fork head was being force-updated while release CI was running. #4974 preserves your feature commits/authorship and supersedes the dead-code-only follow-up with removal of the unused helpers, so the repository stays at its 482/482 budget. I have disabled auto-merge here to avoid racing the mutable head; I’ll close this PR only after #4974 lands.

[SparkofSpike]

I just saw your commit — it aligns perfectly with what I was thinking! I was actually about to handle the $ swallowing issue minutes ago. To be honest, this is one of my first times contributing to an open-source project, and the fact that we came up with the same idea independently feels amazing.
Since you're taking it from here, I'll step back for now — it's already past midnight here. I'll take a look at your code tomorrow and see if there are any features I can add. Thanks for your hard work!

[Hmbown]

Landed through stable integration PR #4974 in merge 135001271ad563dbb298249325dc66d1146e084f, preserving your feature commits and authorship. Thank you for the contribution and the quick follow-up fixes.