getMimeTypes() race condition results in content getting served as xhtml and failing in safari

### Expected Behavior

# Grails core should not silently fall back to createDefaults() in getMimeTypes() — when there's no request, it should defer caching, not poison it.

`org.grails.web.mime.HttpServletResponseExtension.getMimeTypes()`

```java
public static MimeType[] getMimeTypes() {
if (mimeTypes == null) { // ← static field, populated once
webRequest = GrailsWebRequest.lookup(); // ← thread-local request lookup
ApplicationContext ctx = webRequest?.getApplicationContext();
if (ctx != null) {
// CORRECT PATH: read app config via Spring
mimeTypes = ctx.getBean(MimeUtility).getKnownMimeTypes();
loadMimeTypeConfig(ctx.getBean(GrailsApplication).config);
} else {
// WRONG-FALLBACK PATH:
mimeTypes = MimeType.createDefaults(); // [XHTML, HTML, XML, ...]
}
}
return mimeTypes;
}
```

### Actual Behaviour

_No response_

### Steps To Reproduce

_No response_

### Environment Information

_No response_

### Example Application

_No response_

### Version

7.0.10

Start in org.grails.web.mime.HttpServletResponseExtension.getMimeTypes() and inspect how the static mimeTypes field is initialized when GrailsWebRequest.lookup() finds no request. Reproduce or test concurrent and requestless access, then verify that application-configured MIME types are not replaced by defaults and that caching is deferred until an application context is available.

Written by the indexing model from the issue text.