feat(HAI-003): render task descriptions as markdown in dashboard

- Add react-markdown and remark-gfm dependencies
- Replace pre element with ReactMarkdown in TaskDetailModal
- Add markdown prose styles optimized for dark theme
- Regenerate pnpm-lock.yaml to resolve merge conflicts

packages/dashboard/package.json

@@ -16,7 +16,9 @@
     "express": "^5.1.0",
     "lucide-react": "^1.7.0",
     "react": "^19.0.0",
-    "react-dom": "^19.0.0"
+    "react-dom": "^19.0.0",
+    "react-markdown": "^10.1.0",
+    "remark-gfm": "^4.0.1"
   },
   "devDependencies": {
     "@types/express": "^5.0.0",