ci(ci): add SRS_ADMIN_KEY env var and documentation to CI workflows

.github/workflows/close-topics.yml

@@ -1,5 +1,10 @@
 name: Close Topics
 
+# No D1 push here, unlike Close Solved: D1 stores no topic completion column.
+# Phase progress, the gate pools and the charts all derive from the problem
+# rows, which close-solved already logs — a topic is finished exactly when its
+# core problems are, so there is nothing left to reconcile.
+
 on:
   # Close Solved closes problem issues with GITHUB_TOKEN, and token-driven
   # closes never fire `issues` events — so chain off its run instead.