feat(mobile-web): render math formulas with katex in chat markdown

[BingCHuanJ]

Summary

Adds KaTeX math rendering support (remark-math and rehype-katex) to chat markdown messages in mobile-web. It supports inline ($...$, \(...\)) and block ($$...$$, \[...\]) LaTeX formulas with mobile-responsive horizontal scrolling.

Type and Areas

Type: Feature

Areas: mobile web

Motivation / Impact

Currently, LaTeX math formulas sent in remote control chats are displayed as raw text (e.g. $\alpha$ or $$\sum_{i=1}^n x_i$$), making technical discussions and math responses hard to read on mobile devices.

This PR adds:

• TeX formula rendering using katex, remark-math, and rehype-katex.
• Delimiter normalization (\(...\) -> $...$, \[...\] -> $$...$$) with code block protection (safe replacement avoiding string substitution patterns like $$).
• Responsive styling for .katex-display with horizontal scrolling and max-width bounds to prevent layout overflow on narrow mobile screens.

Verification

• pnpm --dir src/mobile-web run type-check: passed cleanly with zero type errors.
• pnpm --dir src/mobile-web run test:ui-components: passed (17/17 tests passing, including delimiter normalization, code block isolation, and math plugin styling tests).
• node --test tests/host-dialog-queue-browser.test.mjs: passed browser verification for KaTeX formula DOM generation.
• node --test scripts/audit-theme-colors.test.mjs: passed (32/32 tests passing).
• pnpm run check:repo-hygiene: passed all product identity, version synchronization, and repository hygiene audits.

Reviewer Notes

• Uses katex/dist/katex.min.css bundled with font handling compatible with mobile assets.
• Formula display blocks (.katex-display) are constrained to viewport bounds with -webkit-overflow-scrolling: touch for smooth touch scrolling.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.