chore: add Dependabot config for weekly npm updates

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

.github/dependabot.yml

@@ -0,0 +1,9 @@
+version: 2
+updates:
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      dev-dependencies:
+        dependency-type: "development"