feat: add Markdown rendering to text segments

- Add react-markdown + remark-gfm for GFM-compatible markdown rendering
- Create MarkdownRenderer component with custom Tailwind-styled elements
- Update TextSegmentView to render markdown instead of plain text
- Update LongTextView to render markdown when expanded
- Fix Lucide icon type in DocumentCard

package.json

@@ -12,7 +12,9 @@
   "dependencies": {
     "lucide-react": "^0.400.0",
     "react": "^18.3.1",
-    "react-dom": "^18.3.1"
+    "react-dom": "^18.3.1",
+    "react-markdown": "^10.1.0",
+    "remark-gfm": "^4.0.1"
   },
   "devDependencies": {
     "@types/react": "^18.3.3",