ci: add 7-day cooldown to dependabot updates

Throttle dependabot PRs to reduce noise from frequent minor version
bumps across all package ecosystems.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: rtibblesbot

.github/dependabot.yml

@@ -9,6 +9,8 @@ updates:
       interval: "weekly"
       day: "friday"
       time: "00:00"
+    cooldown:
+      days: 7
   # Maintain dependencies for Github Actions
   - package-ecosystem: "github-actions"
     directory: "/"
@@ -20,3 +22,5 @@ updates:
       github:
         patterns:
           - "actions/*"
+    cooldown:
+      days: 7