fix(ui) latex dollar render

[8Nothing8]

Issue for this PR

Closes #37326, #38030

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

#34850 intentionally removed bare $...$ math to avoid false positives in currency and code, but its block rule also stopped matching single-line $$...$$.

This PR keeps bare $...$ disabled and adds display-math support for:

• $$...$$, single or multi-line
• \[...\], single or multi-line

Existing \(...\) inline math remains unchanged.

How did you verify your code works?

(Verification)

• bun typecheck in packages/ui
• bun test in packages/ui (9 passing)

Screenshots / recordings

Checklist

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

[github-actions]

Hey! Your PR title Fix latex dollar render doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found a potentially related PR:

Related PR:

• fix(app): render [...] LaTeX display math delimiters (fix(app): render \[...\] LaTeX display math delimiters #35951)
  fix(app): render \[...\] LaTeX display math delimiters #35951

This PR is related because it addresses LaTeX display math rendering with \[...\] delimiters, which is one of the features added in the current PR #38829. However, since the current PR (38829) closes issues #37326 and #38030 and extends the math rendering support beyond what #35951 does (adding $$...$$ in addition to \[...\]), this appears to be a follow-up improvement rather than a true duplicate.

No duplicate PRs found.