ci(dependabot): enable automated dependency updates

gomod (grouped golang.org/x/* and chainreactors/*) plus github-actions where present. No ignore on chainreactors/* so inter-repo deps are auto-updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

.github/dependabot.yml

@@ -0,0 +1,35 @@
+version: 2
+updates:
+  - package-ecosystem: gomod
+    directory: "/"
+    schedule:
+      interval: weekly
+      day: monday
+      time: "04:00"
+      timezone: Asia/Shanghai
+    open-pull-requests-limit: 10
+    labels:
+      - dependencies
+      - go
+    commit-message:
+      prefix: deps
+    groups:
+      golang-x:
+        patterns:
+          - "golang.org/x/*"
+      chainreactors:
+        patterns:
+          - "github.com/chainreactors/*"
+
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: weekly
+      day: monday
+      time: "04:30"
+      timezone: Asia/Shanghai
+    labels:
+      - dependencies
+      - github-actions
+    commit-message:
+      prefix: deps