Consider updating for Inertia 3.x

The reason for wanting 3.x support is that I wanted to try enabling SSR and found that `npm install @inertiajs/vite` doesn't work since:
> npm error Found: vite@6.2.0
npm error node_modules/vite
npm error dev vite@"^6.2.0" from the root project
npm error
npm error Could not resolve dependency:
npm error peer vite@"^7.0.0 || ^8.0.0" from @inertiajs/vite@3.1.1

I could see no appropriate version of that package when [looking on npm](https://www.npmjs.com/package/@inertiajs/vite?activeTab=versions).

_**Note:**_ this was after noticing that the docs for SSR between the two versions is different: [V2](https://inertiajs.com/docs/v2/advanced/server-side-rendering) vs. [V3](https://inertiajs.com/docs/v3/advanced/server-side-rendering).

Start by inspecting the example application's npm dependency configuration and its SSR setup, then compare the Inertia v2 and v3 SSR documentation linked in the issue. Confirm whether the Vite and @inertiajs/vite versions can be aligned without breaking the Spring and React example; done means the project installs successfully and SSR follows the applicable Inertia 3.x setup.

Written by the indexing model from the issue text.