Add Quickstart group with Installation, Hello World, Full Example sub-entries

Author: claude

docs/.vitepress/config.mjs

@@ -106,9 +106,14 @@ export default defineConfig({
         items: [
           { text: "Introduction", link: "/get_started/about" },
           { text: "Use Cases", link: "/get_started/use_cases" },
-          { text: "Installation", link: "/get_started/quickstart" },
-          { text: "Hello World", link: "/get_started/hello_world" },
-          { text: "Full Example", link: "/get_started/full_example" },
+          {
+            text: "Quickstart",
+            items: [
+              { text: "Installation", link: "/get_started/quickstart" },
+              { text: "Hello World", link: "/get_started/hello_world" },
+              { text: "Full Example", link: "/get_started/full_example" },
+            ],
+          },
           { text: `What's Next?`, link: "/get_started/next" },
         ],
       },