feat: render LaTeX math as Unicode in TUI

[Cl-VII]

Issue for this PR

Related to #40508 (V2 TUI LaTeX rendering). This PR implements the TUI side for current V1/V2 TUI markdown rendering.

Type of change

• New feature

What does this PR do?

The web/desktop UI already renders LaTeX math via KaTeX (packages/ui/src/context/marked-parser.tsx). The TUI had no equivalent: formulas in model replies showed raw LaTeX source (e.g. $y = \beta_0 + \beta_1 x + \varepsilon$), with $/*/_ interfering with markdown styling.

This PR adds a marked extension (packages/tui/src/markdown/math-extension.ts) that recognizes inline $...$ and block $$... math and converts the body to readable Unicode via the zero-dependency latex2unicode package (data-driven symbol tables generated from the official unicode-math and KaTeX sources). The extension is passed to the component in the session view through the new extensions option on MarkdownRenderable (anomalyco/opentui#1345).

Edge cases handled:

• $ followed by digits or whitespace ($0.02, $5) is treated as currency/placeholder, not math
• Unclosed $ does not swallow the rest of the text
• Escaped $ inside math works
• Unrecognized LaTeX commands fall back to plain text, so no content is lost

Example output: The model = \beta_0 + \beta_1 x + \varepsilon$ is linear renders as The model 𝑦 = β₀ + β₁𝑥 + ε is linear.

How did you verify your code works?

• Tokenizer unit tests: �un test src/markdown/math-extension.test.ts (6 tests: inline math, currency guard, escaped dollar, block math, empty body, start positions) - all pass
• End-to-end: built opentui core locally (incl. native Zig build on Windows) and verified MarkdownRenderable with the math extension produces a math token with the converted Unicode text
• latex2unicode package: 82 tests pass (greek letters, sub/superscripts, fractions, roots, matrices, display-preference relations, econometrics formulas)

Screenshots / recordings

N/A - terminal output; verification was done via token inspection (the TUI text renderer outputs the Unicode string directly).

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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[Cl-VII]

Author requested removal of all latex-related uploads.