fix TanStack Router basepath for production subpath deployment

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/client/src/main.tsx

@@ -4,7 +4,8 @@ import { createRoot } from "react-dom/client"
 import { RouterProvider, createRouter } from "@tanstack/react-router"
 import { routeTree } from "./routeTree.gen"
 
-const router = createRouter({ routeTree })
+const basepath = import.meta.env.BASE_URL.replace(/\/$/, "") || "/"
+const router = createRouter({ routeTree, basepath })
 
 declare module "@tanstack/react-router" {
 	interface Register {