docs: refresh screenshots for the unified UI, add directory.png

Screenshots were still showing the pre-unification nav (Dashboard/Sites/
Integrations); replace with the current Users/Groups/Directory/Executive
shell and add a directory.png for the new consolidated inventory page.
Fix a couple of stale "Integrations page" / "Sites" references in the
concept docs to match.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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/Integrations
+people in the `app_sso_admin` group can see the Users/Groups/Directory/Executive
 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