fix(delete): review follow-ups — admin Deleted filter, guest gate, dialog spacing

- Admin /users gains a Deleted scope (between People and Robots); every other scope now
  hides tombstoned accounts (deleted_at filter in UserFilter).
- Admin delete-user is offered for any non-deleted account (drop the not-guest gate, so a
  stale is_guest account can still be tombstoned).
- Harden EmailService.ConfirmCode to ClearGuest — defence-in-depth so no confirmed-email
  path leaves is_guest set (the currently-live paths already do).
- Space the delete/change dialog's action row from its input field.
Integration tests: the Deleted filter scoping + ConfirmCode guest promotion.

backend/internal/account/email.go

@@ -206,6 +206,11 @@ func (s *EmailService) ConfirmCode(ctx context.Context, accountID uuid.UUID, ema
 	if err := s.store.confirmEmailIdentity(ctx, conf.id, accountID, addr, s.now()); err != nil {
 		return Account{}, err
 	}
+	// Binding the first confirmed email promotes a guest to a durable account, matching the
+	// link and deeplink flows (defence-in-depth: no confirmed-email path leaves is_guest set).
+	if err := s.store.ClearGuest(ctx, accountID); err != nil {
+		return Account{}, err
+	}
 	return s.store.GetByID(ctx, accountID)
 }