ci: label Dependabot pull requests

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W14eEfXdK5DYzv43MazryE

Author: claude

.github/dependabot.yml

@@ -16,3 +16,5 @@ updates:
           - "*"
     commit-message:
       prefix: "ci"
+    labels:
+      - Dependencies