Run Dependabot updates weekly

We now review dependency updates weekly rather than daily, so daily
update runs only generate churn. Check for updates once a week on
Monday morning instead.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: horgh

.github/dependabot.yml

@@ -3,15 +3,17 @@ updates:
   - package-ecosystem: composer
     directory: /
     schedule:
-      interval: daily
+      interval: weekly
+      day: monday
       time: '14:00'
     open-pull-requests-limit: 10
     cooldown:
       default-days: 7
   - package-ecosystem: github-actions
     directory: /
     schedule:
-      interval: daily
+      interval: weekly
+      day: monday
       time: '14:00'
     cooldown:
       default-days: 7