[ci] add ci-monitor workflow (#10898)

.github/workflows/ci-monitor.yml

+name: CI Monitor
+
+on:
+  schedule:
+    # Run every 6 hours at 00:00, 06:00, 12:00, 18:00 UTC
+    - cron: '0 */6 * * *'
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+    inputs:
+      limit:
+        description: 'Number of CI runs to analyze'
+        required: false
+        default: '1000'
+        type: string
+
+concurrency:
+  group: ci-monitor-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  ci-monitor:
+    if: github.repository == 'sgl-project/sglang'|| github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.9'
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install requests
+
+      - name: Run CI Analysis
+        env:
+          GITHUB_TOKEN: ${{ secrets.GH_PAT_FOR_NIGHTLY_CI }}
+          PYTHONUNBUFFERED: 1
+          PYTHONIOENCODING: utf-8
+        run: |
+          cd scripts/ci_monitor
+          python ci_analyzer.py --token $GITHUB_TOKEN --limit ${{ github.event.inputs.limit || '1000' }} --output ci_analysis_$(date +%Y%m%d_%H%M%S).json
+
+      - name: Upload Analysis Results
+        uses: actions/upload-artifact@v4
+        with:
+          name: ci-analysis-results-${{ github.run_number }}
+          path: scripts/ci_monitor/ci_analysis_*.json
+          retention-days: 30