fix(admin): unified user search across live + deleted, incl. the retention journal

The email/name/external-id search was scoped to one tab and only looked in the live
identities table, so a deleted account (whose credentials moved to retained_identities on
deletion) could not be found by the email/id it held. Now a people search spans live and
deleted accounts in one query (robots only on the Robots tab) and also matches the
retention journal and the retained real name; results carry a 'deleted' badge. Integration
test: a deleted account is found by its held email and external id.

backend/internal/adminconsole/templates/pages/users.gohtml

@@ -19,7 +19,7 @@
 {{range .Items}}
 <tr>
 <td><a href="/_gm/users/{{.ID}}">{{.ID}}</a></td>
-<td>{{.DisplayName}}{{if .Guest}} <span class="pill">guest</span>{{end}}{{if .FlaggedHighRate}} <span class="pill">high-rate</span>{{end}}</td>
+<td>{{.DisplayName}}{{if .Deleted}} <span class="pill">deleted</span>{{end}}{{if .Guest}} <span class="pill">guest</span>{{end}}{{if .FlaggedHighRate}} <span class="pill">high-rate</span>{{end}}</td>
 <td>{{.Kind}}</td>
 <td>{{.Language}}</td>
 <td>{{.CreatedAt}}</td>