Admin route to delete an active account on request #471

Summary

After #412, the admin ghost-account delete refuses any account that is not a ghost. So there is no route that deletes an active account when its owner asks for that under the privacy promise. An operator must do it by hand today.

• Source: the Clear the public profile when an account is soft-deleted #427 build, 2026-10-09. Clear the public profile when an account is soft-deleted #427 added one private soft-delete helper, softDeleteUsers in apps/hocuspocus.server/src/api/services/adminGhostAccounts.service.ts. Both existing soft-delete paths call it.
• Manual path until this lands: clear the same fields the helper clears. Set deleted_at, null full_name, avatar_url and avatar_updated_at, set profile_data to {}, set username to deleted_ plus 12 hex characters of the id, remove the {id}/ objects in user_avatars, and ban the user.

Fix

1. Add an admin route, for example DELETE /api/admin/users/:id, behind the existing admin guard. Validate :id as a uuid.
2. Export softDeleteUsers and call it for that one id.
3. Refuse an admin. Revoke admin access first through public.admin_revoke_admin.
4. Add the route to the OpenAPI admin paths and to apps/hocuspocus.server/API.md.

Acceptance

• An admin can soft-delete one active, non-admin account, and every field above is cleared.
• The route refuses an admin account with 409.
• A non-uuid id answers the house 400.