Feature Request: Restore a one-click Open WP Admin action

### What

Please add a clearly visible action that opens the selected site's WordPress Admin dashboard directly, ideally with automatic authentication as supported by the previous Studio interface.

### Why

In the new interface, the most visible browser action appears to open only the site's front end. I can no longer easily find a direct shortcut to WordPress Admin.

When authentication is required, my current workflow is:

1. Open the site in a browser.
2. Find the admin credentials in Studio's settings.
3. Copy the password.
4. Manually navigate to the WordPress login page.
5. Enter or paste the credentials.

This adds unnecessary steps to a task performed frequently while developing and debugging local WordPress sites.

### How

Add an **Open WP Admin** action beside the front-end preview link or within the site-title dropdown. Ideally, it should open `/wp-admin/` and automatically authenticate the local administrator.

Start by locating the current front-end preview action and site-title dropdown in the TypeScript desktop interface, then trace how local administrator credentials are exposed in Studio settings and how browser links are opened. Done means the selected site has a visible Open WP Admin action that opens /wp-admin/ and uses the supported automatic authentication flow when needed.

Written by the indexing model from the issue text.