[chore] Create dependabot.yml

.github/dependabot.yml

@@ -0,0 +1,36 @@
+version: 2
+updates:
+  # main → 보안 업데이트만 (limit: 0 = 보안 PR만 통과)
+  - package-ecosystem: npm
+    directory: /frontend
+    schedule:
+      interval: weekly
+    open-pull-requests-limit: 0
+
+  - package-ecosystem: gradle
+    directory: /backend
+    schedule:
+      interval: weekly
+    open-pull-requests-limit: 0
+
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly
+    open-pull-requests-limit: 5
+
+  # develop-fe → 프론트엔드 정기 버전 업데이트 PR
+  - package-ecosystem: npm
+    directory: /frontend
+    target-branch: develop-fe
+    schedule:
+      interval: weekly
+    open-pull-requests-limit: 5
+
+  # develop/be → 백엔드 정기 버전 업데이트 PR
+  - package-ecosystem: gradle
+    directory: /backend
+    target-branch: develop/be
+    schedule:
+      interval: weekly
+    open-pull-requests-limit: 5