Custom vite middleware is not executed for CSS files

### Command

serve

### Description

We are in the process of migrating from using webpack to esbuild/vite.

For development purposes, we need a way to dynamically switch from one theme to another. At this point, we have achieved it by proxying CSS or image files depending on the host name.

After switching to Vite, it turned out that it could work the same, apart from the fact that for CSS resources, our middleware is never executed.

I found a piece of code that seems to be the root cause. The `AngularMemoryPlugin` handles CSS files in a specific way and never executes `next()`, which terminates the middleware chain.

https://github.com/angular/angular-cli/blob/3d7b5f78bdab834cb50c441296c9bf31f7a5e764/packages/angular_devkit/build_angular/src/tools/vite/angular-memory-plugin.ts#L163-L178

### Describe the solution you'd like

Ideally middleware chain should not be terminated in `AngularMemoryPlugin` for stylesheets (ie. `next()` should be called)

### Describe alternatives you've considered

In the worst case scenario, we will find another solution for our use case. However, since the issue only pertains to CSS files, it would be really helpful if the middleware is executed for these files as well.

从 packages/angular_devkit/build_angular/src/tools/vite/angular-memory-plugin.ts 中第 163–178 行附近的 CSS 处理开始，跟踪 Vite middleware 链如何为样式表完成。确认此更改在保留 CSS 提供功能的同时，允许自定义 middleware 处理 CSS 资源，然后验证 serve 命令的行为。

由索引模型根据 Issue 内容生成。