fix(ci): Add concurrency control to prevent queue buildup

沿用 AIOPS 設計:
- cancel-in-progress: true - 新 commit 自動取消舊 workflow
- workflow_dispatch 支援手動觸發
- concurrency group 隔離不同分支

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/ci.yaml

@@ -5,6 +5,12 @@ on:
     branches: [main]
   pull_request:
     branches: [main]
+  workflow_dispatch:
+
+# 沿用 AIOPS 設計: 新 commit 自動取消舊 workflow
+concurrency:
+  group: ci-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 
 env:
   NODE_VERSION: '20'