Update Mattermost to 12.0 (#2202)

* Initial plan

* Update Mattermost metadata to 12.0

Co-authored-by: chendelin1982 <16741975+chendelin1982@users.noreply.github.com>

* Keep Mattermost README diff minimal

Co-authored-by: chendelin1982 <16741975+chendelin1982@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: chendelin1982 <16741975+chendelin1982@users.noreply.github.com>

Author: Copilot

apps/mattermost/.env

@@ -1,6 +1,6 @@
 W9_REPO=mattermost/mattermost-team-edition
 W9_DIST=community
-W9_VERSION=11.11
+W9_VERSION=12.0
 
 # Canonical semantics live in docs/w9-env-spec.md.
 # This template controls layout; the spec controls meaning and decision rules.

apps/mattermost/CHANGELOG.md

@@ -1,5 +1,9 @@
 # CHANGELOG
 
+## 2026-10-30
+
+- Update Mattermost Team Edition from `11.11` to `12.0`.
+
 ## 2026-10-12
 
 - Pin Mattermost Team Edition from the floating `11.11` line to the current stable patch `11.11.1` for deterministic deployments.

apps/mattermost/README.md

@@ -33,7 +33,7 @@ Apps run as containers; rebuild after any configuration change.
 
 ### Version Support
 
-Supported versions: 11.11.1.
+Supported versions: 12.0.
 
 
 ### Ports
@@ -77,7 +77,7 @@ Configuration files live inside the image; mount a single file read-only to over
 
 - [Official docs](https://docs.mattermost.com/deployment-guide/server/docker-troubleshooting.html)
 
-- [Official docs](https://docs.mattermost.com/product-overview/mattermost-v11-changelog.html)
+- [Official docs](https://docs.mattermost.com/product-overview/mattermost-v12-changelog)
 
 
 <!-- W9_TROUBLESHOOT_START -->

apps/mattermost/variables.json

@@ -7,14 +7,14 @@
     "docs": [
       "https://docs.mattermost.com/install/install-docker.html",
       "https://docs.mattermost.com/deployment-guide/server/docker-troubleshooting.html",
-      "https://docs.mattermost.com/product-overview/mattermost-v11-changelog.html"
+      "https://docs.mattermost.com/product-overview/mattermost-v12-changelog"
     ]
   },
   "edition": [
     {
       "dist": "community",
       "version": [
-        "11.11"
+        "12.0"
       ]
     }
   ],