ci(codeql): cron weekly→monthly (cut 3, standards#288) (#76)

Per standards#286 canonical (cut 3, Option B). PR-trigger runs
unchanged.

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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/codeql.yml

@@ -14,7 +14,7 @@ on:
   pull_request:
     branches: [main, master]
   schedule:
-    - cron: '0 6 * * 1'
+    - cron: '0 6 1 * *'   # monthly 1st 06:00 UTC
 
 # Estate guardrail: cancel superseded runs so re-pushes / rebased PR
 # updates do not pile up queued runs against the shared account-wide