ci: switch trigger to manual workflow_dispatch for decommission docs phase [skip ci]

Phase 1 of the decommission plan produces documentation-only commits;
push:main would rebuild and redeploy all three images on each one.
The workflow is kept (not deleted) and can still be run manually from
the Gitea Actions UI.

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

.gitea/workflows/ci.yml

@@ -1,9 +1,10 @@
 name: CI/CD
 
+# Decommission (2026-07): trigger switched from push:main to manual only, so
+# documentation commits don't rebuild/redeploy images. Run from the Gitea UI
+# (Actions → Run workflow) if a rebuild is ever needed again.
 on:
-  push:
-    branches:
-      - main
+  workflow_dispatch:
 
 env:
   REGISTRY: gitea.gitea.svc.cluster.local:3000