feat: render markdown in AI Chat assistant responses

Replace regex-based bold/newline rendering with react-markdown + remark-gfm
+ rehype-highlight for full markdown support: bold, code blocks with syntax
highlighting, bullet/ordered lists, headers, blockquotes, links, tables.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/AIChatPanel.tsx

@@ -9,6 +9,7 @@ import {
   buildSystemPrompt,
 } from '../utils/ai-chat'
 import { useAIChat } from '../hooks/useAIChat'
+import { MarkdownContent } from './MarkdownContent'
 
 // --- Sub-components ---
 
@@ -101,10 +102,7 @@ function ContextSearchDropdown({
 function AssistantMessage({ msg, onRetry }: { msg: ChatMessage; onRetry: () => void }) {
   return (
     <div>
-      <div style={{ fontSize: 13, lineHeight: 1.6, whiteSpace: 'pre-wrap' }}
-        dangerouslySetInnerHTML={{
-          __html: msg.content.replace(/\*\*(.*?)\*\*/g, '<strong>$1</strong>').replace(/\n/g, '<br/>'),
-        }} />
+      <MarkdownContent content={msg.content} />
       <div className="flex items-center gap-3" style={{ marginTop: 4 }}>
         <button className="border-none bg-transparent p-0 text-muted-foreground cursor-pointer hover:underline"
           style={{ fontSize: 11 }} onClick={() => navigator.clipboard.writeText(msg.content)}>
@@ -126,10 +124,7 @@ function AssistantMessage({ msg, onRetry }: { msg: ChatMessage; onRetry: () => v
 function StreamingContent({ content }: { content: string }) {
   return (
     <div style={{ marginBottom: 12 }}>
-      <div style={{ fontSize: 13, lineHeight: 1.6, whiteSpace: 'pre-wrap' }}
-        dangerouslySetInnerHTML={{
-          __html: content.replace(/\*\*(.*?)\*\*/g, '<strong>$1</strong>').replace(/\n/g, '<br/>'),
-        }} />
+      <MarkdownContent content={content} />
     </div>
   )
 }

src/components/MarkdownContent.test.tsx

@@ -0,0 +1,75 @@
+import { describe, it, expect } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import { MarkdownContent } from './MarkdownContent'
+
+describe('MarkdownContent', () => {
+  it('renders bold text', () => {
+    render(<MarkdownContent content="Hello **world**" />)
+    const strong = screen.getByText('world')
+    expect(strong.tagName).toBe('STRONG')
+  })
+
+  it('renders inline code', () => {
+    render(<MarkdownContent content="Use `console.log`" />)
+    const code = screen.getByText('console.log')
+    expect(code.tagName).toBe('CODE')
+  })
+
+  it('renders fenced code blocks', () => {
+    const { container } = render(<MarkdownContent content={'```js\nconst x = 1\n```'} />)
+    const pre = container.querySelector('pre')
+    expect(pre).toBeTruthy()
+    expect(pre!.textContent).toContain('const x = 1')
+  })
+
+  it('renders unordered lists', () => {
+    const { container } = render(<MarkdownContent content={'- one\n- two\n- three'} />)
+    const items = container.querySelectorAll('li')
+    expect(items).toHaveLength(3)
+    expect(items[0].textContent).toBe('one')
+  })
+
+  it('renders ordered lists', () => {
+    const { container } = render(<MarkdownContent content={'1. first\n2. second'} />)
+    const ol = container.querySelector('ol')
+    expect(ol).toBeTruthy()
+    expect(ol!.querySelectorAll('li')).toHaveLength(2)
+  })
+
+  it('renders headers', () => {
+    render(<MarkdownContent content="## Section Title" />)
+    const h2 = screen.getByText('Section Title')
+    expect(h2.tagName).toBe('H2')
+  })
+
+  it('renders links', () => {
+    render(<MarkdownContent content="[Click here](https://example.com)" />)
+    const link = screen.getByText('Click here') as HTMLAnchorElement
+    expect(link.tagName).toBe('A')
+    expect(link.getAttribute('href')).toBe('https://example.com')
+  })
+
+  it('renders mixed markdown', () => {
+    const { container } = render(<MarkdownContent content={'**Bold** and `code` and\n\n- item'} />)
+    expect(screen.getByText('Bold').tagName).toBe('STRONG')
+    expect(screen.getByText('code').tagName).toBe('CODE')
+    expect(container.querySelector('li')).toBeTruthy()
+  })
+
+  it('wraps content in .ai-markdown container', () => {
+    const { container } = render(<MarkdownContent content="Hello" />)
+    expect(container.querySelector('.ai-markdown')).toBeTruthy()
+  })
+
+  it('renders plain text without crashing', () => {
+    render(<MarkdownContent content="Just plain text" />)
+    expect(screen.getByText('Just plain text')).toBeTruthy()
+  })
+
+  it('renders blockquotes', () => {
+    const { container } = render(<MarkdownContent content="> A quote" />)
+    const bq = container.querySelector('blockquote')
+    expect(bq).toBeTruthy()
+    expect(bq!.textContent).toContain('A quote')
+  })
+})

src/components/MarkdownContent.tsx

@@ -0,0 +1,18 @@
+import { memo, useMemo } from 'react'
+import Markdown from 'react-markdown'
+import remarkGfm from 'remark-gfm'
+import rehypeHighlight from 'rehype-highlight'
+
+const REMARK_PLUGINS = [remarkGfm]
+const REHYPE_PLUGINS = [rehypeHighlight]
+
+export const MarkdownContent = memo(function MarkdownContent({ content }: { content: string }) {
+  const rendered = useMemo(() => (
+    <div className="ai-markdown">
+      <Markdown remarkPlugins={REMARK_PLUGINS} rehypePlugins={REHYPE_PLUGINS}>
+        {content}
+      </Markdown>
+    </div>
+  ), [content])
+  return rendered
+})