Add Service Account experiment

[Jameswlepage]

What?

Exploring the concept of a true "service account"; something a real user can create as a way for a service, like Claude Code, an automation tool, or an API can use to interact with WP in a safe, auditable manner. It's an actual new user type, and I've hacked a bit to get some of the UI "core-like". If it moves closer to a core feature, we'll need to rethink but for now, I'm interested in thinking around ... "do we need this"?

• Adds the Service Account experiment (role, admin UI, REST endpoints).
• Registers the experiment in the loader.
• Adds integration coverage and documentation.

Why?

Service accounts enable automation and non-interactive access while keeping user activity traceable in logs and revisions. This is core-aligned functionality that needs dedicated UX and API support.

How?

• Introduce the Service Account experiment classes and manager.
• Add admin UI customizations for service account creation/editing.
• Add REST endpoints for service account CRUD and app-password regeneration.
• Add docs and integration tests.

Testing Instructions

1. Enable the Service Accounts experiment.
2. Go to Users > Add New, select the Service role, enter a service account name.
3. Confirm username/email auto-populate; create the user.
4. In Users list, verify the service account shows and the Service Accounts view has an accurate count.
5. Edit the service account and create an Application Password in the section below.
6. REST: POST /wp/v2/service-accounts, GET /wp/v2/service-accounts, POST /wp/v2/service-accounts/{id}/app-password.

Testing Instructions for Keyboard

1. Use Tab to reach the Role dropdown on Users > Add New.
2. Use arrow keys to select Service role, Tab to the Service account name field.
3. Type a name, Tab through username/email (read-only) and password.
4. Tab to submit and press Enter.
5. On the edit screen, Tab to the Application Passwords section and generate a password.

Screenshots or screencast

[Jameswlepage]

Note; we will need to remove provider specific labels (Claude Code) if this gets closer to being a real thing.