docs: add 6 missing legacy redirect entries to active-redirects.json (#38317)

Six legacy Sphinx URLs are still linked from the Mattermost webapp (per
the failing check-external-links CI in the webapp), but they had no
corresponding entry in active-redirects.json, so @docusaurus/plugin-
client-redirects emitted no stub for them and every cold request 404s.

The targets are taken from the equivalent redirects in the old Sphinx
site's source/redirects.py (which is what the migration extraction
should have picked up in the first place), verified to resolve to real
MDX pages under docs/main/:

  /about/cloud-subscriptions                    -> /product-overview/cloud-subscriptions
  /collaborate/format-messages                  -> /end-user-guide/collaborate/format-messages
  /configure/environment-configuration-settings -> /administration-guide/configure/environment-configuration-settings
  /deployment/admin-roles                       -> /administration-guide/onboard/delegated-granular-administration
  /deployment/ldap-group-sync                   -> /administration-guide/onboard/ad-ldap-groups-synchronization
  /guides/administration                        -> /administration-guide/administration-guide-index

Bumps _meta.active from 741 to 747.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/site/sidebars/active-redirects.json

@@ -2,7 +2,7 @@
   "_meta": {
     "maintained": "by hand",
     "note": "Legacy Sphinx URL redirects, originally bulk-extracted during the docs migration. Add new entries at the end of the array. `from` must be unique and must not contain an anchor; `to` should point at a page that exists, or the redirect silently dead-ends.",
-    "active": 741
+    "active": 747
   },
   "redirects": [
     {
@@ -2968,6 +2968,30 @@
     {
       "from": "/deployment-guide/server/trouble-postgres",
       "to": "/deployment-guide/server/prepare-database"
+    },
+    {
+      "from": "/about/cloud-subscriptions",
+      "to": "/product-overview/cloud-subscriptions"
+    },
+    {
+      "from": "/collaborate/format-messages",
+      "to": "/end-user-guide/collaborate/format-messages"
+    },
+    {
+      "from": "/configure/environment-configuration-settings",
+      "to": "/administration-guide/configure/environment-configuration-settings"
+    },
+    {
+      "from": "/deployment/admin-roles",
+      "to": "/administration-guide/onboard/delegated-granular-administration"
+    },
+    {
+      "from": "/deployment/ldap-group-sync",
+      "to": "/administration-guide/onboard/ad-ldap-groups-synchronization"
+    },
+    {
+      "from": "/guides/administration",
+      "to": "/administration-guide/administration-guide-index"
     }
   ]
 }