ci(codeql): weekly -> monthly cron (standards#288 cut 3) (#57)

Clean re-do of the stale `cicd/codeql-cron-monthly` branch (42-behind,
conflicting). One-line cron change per the decided estate codeql-monthly
policy. Supersedes #55.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/codeql.yml

@@ -6,7 +6,7 @@ on:
   pull_request:
     branches: [main, master]
   schedule:
-    - cron: '0 6 * * 1'
+    - cron: '0 6 1 * *'   # monthly, 1st 06:00 UTC (standards#288 cut 3)
 # Estate guardrail: cancel superseded runs so re-pushes / rebased PR
 # updates do not pile up queued runs against the shared account-wide
 # Actions concurrency pool. Applied only to read-only check workflows