docs(ci): document protected status contexts

.gitea/workflows/ci.yml

@@ -1,3 +1,7 @@
+# Keep workflow name stable.
+# Branch protection and external CI references rely on:
+# - CI / verify (push)
+# - CI / verify (pull_request)
 name: CI
 
 on:
@@ -9,6 +13,7 @@ on:
 
 jobs:
   verify:
+    # Keep job id stable. Renaming it changes the status context.
     runs-on: ubuntu-latest
     env:
       WORKSPACE_DIR: ${{ github.workspace }}/repo