We should provide better UI for prompt management. There should be an overview of all prompts and prompt fragments in the AI configuration view. Further, we should make it transparent which prompt for which ID is effective and which prompts are overridden.

Also see the following comments from #15236 (review)

With the new workspace related directories, we are able to override existing prompts and existing prompt customizations. However it's very intransparent that this is happening. The AI configuration view should indicate this and ideally even allow to open an editor for the currently "active" prompt file. Can of course be handled in a follow up.

When I want to override the default prompt of an agent, it's difficult to determine which key I need to use as they are only shown as default in the UI. Only by editing them, I can see their key in the customization file name. We should show the key of the prompts in the configuration view and just add a (default) suffix for the default ones. Can of course be handled in a follow up.