chore: Add Dependabot for Gradle plugins

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: runningcode

.github/dependabot.yml

@@ -4,3 +4,7 @@ updates:
     directory: "/"
     schedule:
       interval: weekly
+  - package-ecosystem: "gradle"
+    directory: "/"
+    schedule:
+      interval: weekly