Add cross-app super admin group; rename Executive page to Overview

- app_super_admin is a new cross-app LDAP group (also recognized by proxy
  and jump-host) that grants full admin here regardless of app_sso_admin
  membership: bypassed centrally in utils/permission.js's byGroup, folded
  into GET /api/user/me's isAdmin flag, and added to nav/forceLogin gates
  alongside app_sso_admin.
- Renamed the Executive page to Overview (route, view, API path
  /api/metrics/overview, nav label, docs), keeping /executive as a 301
  redirect alongside the existing /admin, /notifications, /dashboard
  legacy redirects.

docs/concepts-accounts.md

@@ -46,7 +46,7 @@ on, just like anyone else's.
 
 A **group** is just a named list of accounts, used to control access. This
 app has a handful of built-in groups that grant admin powers (e.g. only
-people in the `app_sso_admin` group can see the Users/Groups/Directory/Executive
+people in the `app_sso_admin` group can see the Users/Groups/Directory/Overview
 pages at all), but you can also make your own groups for any app you
 connect — say, a group listing everyone who should be allowed into your
 photo server. Once a group exists, add or remove members from the

docs/index.md

@@ -22,7 +22,7 @@ one command).
 
 ## Screenshots
 
-<a href="images/dashboard.png" target="_blank"><img src="images/dashboard.png" alt="Executive dashboard" width="49%"></a>
+<a href="images/dashboard.png" target="_blank"><img src="images/dashboard.png" alt="Overview dashboard" width="49%"></a>
 <a href="images/users.png" target="_blank"><img src="images/users.png" alt="User list" width="49%"></a>
 <a href="images/groups.png" target="_blank"><img src="images/groups.png" alt="Groups" width="49%"></a>
 <a href="images/directory.png" target="_blank"><img src="images/directory.png" alt="Directory & inventory" width="49%"></a>