Increase container scan frequency from weekly to daily

- Change schedule from 'Monday at 6am UTC' to 'daily at 12pm UTC'
- 12pm UTC = 7am-8am Boston time (depending on DST), allowing same-
  day action on newly discovered CVEs
- Trivy DB updates every 6 hours; daily scans catch CVEs within 24h
  vs up to 7 days with weekly scans
- No cost impact (public repo = unlimited free GHA minutes)

Author: dpark01

.github/workflows/container-scan.yml

@@ -2,8 +2,8 @@ name: Scheduled Container Vulnerability Scan
 
 on:
   schedule:
-    # Weekly scan of main branch mega image every Monday at 06:00 UTC
-    - cron: '0 6 * * 1'
+    # Daily scan of main branch mega image at 12:00 UTC
+    - cron: '0 12 * * *'
   workflow_dispatch:
     inputs:
       test_cve_id: