Better Nuxt/Astro integration

### Description

Currently, it feels like vite-plus and nuxt/astro provide two different interfaces that don't talk to each other. In particular,

1. Nuxt/astro config cannot be used to specify vite+ config (see https://github.com/voidzero-dev/vite-plus/issues/912)
2. `vp dev` and `vp build` don't call the correct nuxt/astro commands (see https://github.com/voidzero-dev/vite-plus/issues/1123)

(both issues were raised before but are now closed although they are not fixed)

### Suggested solution

ad 1: create an offical vite+ nuxt/astro module that reads the vite+ config from `nuxt/astro.config` and exposes it in the temporary framework folder (eg `.nuxt/viteplus.config.mjs`), and in vite+ add a fallback to those known locations if a main vite.config is missing.

ad 2: recognize that the project is using nuxt/astro, and then call the correct framework commands

### Alternative

_No response_

### Additional context

_No response_

### Validations

- [x] Read the [Contributing Guidelines](https://github.com/voidzero-dev/vite-plus/blob/main/CONTRIBUTING.md).
- [x] Confirm this request is for Vite+ itself and not for Vite, Vitest, tsdown, Rolldown, or Oxc.
- [x] Check that there isn't already an issue requesting the same feature.