fix: increase npm cooldown default-days to 7 for zizmor compliance

zizmor requires default-days >= 7. Semver-specific days still apply
for major (14d), minor (3d), and patch (3d).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: chrisreddington

.github/dependabot.yml

@@ -18,7 +18,7 @@ updates:
     schedule:
       interval: weekly
     cooldown:
-      default-days: 3
+      default-days: 7
       semver-major-days: 14
       semver-minor-days: 3
       semver-patch-days: 3