feat(k8s): CoreDNS GitOps 架構 (ADR-026)

問題: DNS 配置沒有版本控制，手動修改易遺失

架構:
- k8s/k3s-system/coredns-custom.yaml: HelmChartConfig
- CD workflow: k3s-system 路徑偵測 + 自動 apply
- ADR-026: CoreDNS GitOps 管控架構

DNS 上游:
- 使用 8.8.8.8 + 1.1.1.1
- 禁止 /etc/resolv.conf (systemd-resolved)

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

.github/workflows/cd.yaml

@@ -111,6 +111,7 @@ jobs:
     outputs:
       api: ${{ inputs.force_deploy == true && 'true' || steps.filter.outputs.api }}
       web: ${{ inputs.force_deploy == true && 'true' || steps.filter.outputs.web }}
+      k3s-system: ${{ steps.filter.outputs.k3s-system }}
     steps:
       # 2026-03-26: 清理暫存目錄 (temp + pages)
       - name: "Clean Runner temp"
@@ -135,6 +136,8 @@ jobs:
               - 'packages/**'
               - 'package.json'
               - 'pnpm-lock.yaml'
+            k3s-system:
+              - 'k8s/k3s-system/**'
 
   # ==================== 並行建構 API ====================
   build-api:
@@ -280,6 +283,15 @@ jobs:
 
           kubectl apply -k .
 
+      # 2026-03-26: CoreDNS GitOps 同步 (ADR-026)
+      - name: Sync CoreDNS Config
+        if: needs.detect-changes.outputs.k3s-system == 'true'
+        run: |
+          echo "📦 同步 CoreDNS 配置到 K3s..."
+          # HelmChartConfig 是 K8s 資源，直接 apply
+          kubectl apply -f k8s/k3s-system/coredns-custom.yaml
+          echo "✅ CoreDNS 配置已同步"
+
       - name: Wait for rollout
         run: |
           kubectl rollout status deployment/awoooi-web -n awoooi-prod --timeout=300s || true