Chore: Use template literal to comply with Biome linter (TanStack#79)

Switched to template literals to comply with Biome linting rules. Fixes
an issue where scaffold initialization would "fail" when selecting
TanStack Query and tRPC with the Biome toolchain.

<details>
<summary>Output with this problem</summary>
<img width="907" alt="image"
src="https://github.com/user-attachments/assets/794eb0b4-a5bd-4fa6-ba07-e2ac5b11e08a"
/>
</details>

Author: vk0novalov

packages/cta-engine/templates/react/add-on/tanstack-query/assets/src/integrations/tanstack-query/root-provider.tsx.ejs

@@ -13,7 +13,7 @@ function getUrl() {
     if (typeof window !== "undefined") return "";
     return `http://localhost:${process.env.PORT ?? 3000}`;
   })();
-  return base + "/api/trpc";
+  return `${base}/api/trpc`;
 }
 
 export const trpcClient = createTRPCClient<TRPCRouter>({
@@ -67,4 +67,4 @@ export function Provider({ children }: { children: React.ReactNode }) {
     <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
   )
 }
-<% } %>
+<% } %>