feat: migrate ESLint to v9 flat config

- Replace .eslintrc.json with eslint.config.mjs
- Simplify configuration using @antfu/eslint-config
- Add necessary ESLint plugin dependencies
- Disable overly strict style rules
- Set package.json type to module for ESM support
- Fix ESLint disable comment format

🤖 Generated with [Claude Code](https://claude.ai/code)

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

app/components/base/streamdown-markdown.tsx

@@ -0,0 +1,18 @@
+'use client'
+import { Streamdown } from 'streamdown'
+import 'katex/dist/katex.min.css'
+
+interface StreamdownMarkdownProps {
+  content: string
+  className?: string
+}
+
+export function StreamdownMarkdown({ content, className = '' }: StreamdownMarkdownProps) {
+  return (
+    <div className={`markdown-body streamdown-markdown ${className}`}>
+      <Streamdown>{content}</Streamdown>
+    </div>
+  )
+}
+
+export default StreamdownMarkdown