feat: implement AI chat interface with markdown support and model cost tracking

package.json

@@ -31,6 +31,8 @@
     "radix-ui": "^1.4.3",
     "react": "19.2.3",
     "react-dom": "19.2.3",
+    "react-markdown": "^10.1.0",
+    "remark-gfm": "^4.0.1",
     "tailwind-merge": "^3.5.0",
     "zod": "^4.3.6",
     "zustand": "^5.0.11"