feat: Latex support (#929)

* feat: implement LaTeX math rendering via KaTeX

- Add katex, remark-math, and rehype-katex dependencies
- Integrate KaTeX CSS with light/dark theme color overrides
- Wire remark-math and rehype-katex plugins into MarkdownRenderer
- Support inline ($...$) and display ($$...$$) math delimiters
- Add plan and task documentation

* fix(katex): display inline error messages for invalid LaTeX

- Configure rehypeKatex with throwOnError: false to render errors inline
- Use destructive color var for error text
- Update feature documentation with verification results

* chore: remove latex PR artifacts and hardcoded color fallback

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Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/components/chat/MarkdownRenderer.tsx

@@ -3,6 +3,8 @@ import { renderMermaidASCII, renderMermaidSVG } from 'beautiful-mermaid';
 import ReactMarkdown from 'react-markdown';
 import type { Components } from 'react-markdown';
 import remarkGfm from 'remark-gfm';
+import remarkMath from 'remark-math';
+import rehypeKatex from 'rehype-katex';
 import { marked, type Tokens } from 'marked';
 import remend from 'remend';
 import { FadeInOnReveal } from './message/FadeInOnReveal';
@@ -817,7 +819,7 @@ const MarkdownBlockView: React.FC<{
   components: Components;
 }> = React.memo(({ block, components }) => {
   return (
-    <ReactMarkdown remarkPlugins={[remarkGfm]} components={components}>
+    <ReactMarkdown remarkPlugins={[remarkGfm, remarkMath]} rehypePlugins={[[rehypeKatex, { throwOnError: false, errorColor: 'var(--destructive)' }]]} components={components}>
       {block.src}
     </ReactMarkdown>
   );