fix(ci): 修復 Runner _diag/pages 檔案衝突 (徹底解決)

根本原因:
- 41 個殭屍 Runner 進程互相衝突
- _diag/pages 目錄沒有自動清理

解決方案:
- 所有 Workflow Job 第一步清理 _diag/pages
- 覆蓋所有 self-hosted runner jobs

影響範圍:
- runner-healthcheck.yml (2 jobs)
- daily-e2e-health.yaml (1 job)
- nightly-llm.yaml (1 job)
- ci.yaml (9 jobs)
- cd.yaml (已有)

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

.github/workflows/nightly-llm.yaml

@@ -38,6 +38,13 @@ jobs:
     runs-on: [self-hosted, harbor, k8s]
     timeout-minutes: 60  # 1 小時超時
     steps:
+      # 2026-03-29 Claude Code: 修復 _diag/pages 檔案衝突
+      - name: "Clean Runner Diagnostics"
+        run: |
+          RUNNER_ROOT=$(dirname "$(dirname "$RUNNER_TEMP")")
+          rm -rf "$RUNNER_ROOT/_diag/pages" 2>/dev/null || true
+          mkdir -p "$RUNNER_ROOT/_diag/pages" 2>/dev/null || true
+
       - uses: actions/checkout@v4
 
       - name: Setup Python