docs(router): fix the import of StartServer in the SSR guide (#2358)

Since `StartServer` is exporting from `@tanstack/start/server`, the import path should be updated

docs/framework/react/guide/ssr.md

@@ -21,7 +21,7 @@ Non-Streaming server-side rendering is the classic process of rendering the mark
 
 To implement non-streaming SSR with TanStack Router, you will need the following utilities:
 
-- `StartServer` from `@tanstack/start`
+- `StartServer` from `@tanstack/start/server`
   - e.g. `<StartServer router={router} />`
   - Rendering this component in your server entry will render your application and also automatically handle application-level hydration/dehydration and implement the `Wrap` component option on `Router`
 - `StartClient` from `@tanstack/start`
@@ -142,7 +142,7 @@ Here is a complete example of a server entry file that uses all of the concepts
 import * as React from 'react'
 import ReactDOMServer from 'react-dom/server'
 import { createMemoryHistory } from '@tanstack/react-router'
-import { StartServer } from '@tanstack/start'
+import { StartServer } from '@tanstack/start/server'
 import { createRouter } from './router'
 
 export async function render(url, response) {