Add monitoring workflows (#7)

.github/workflows/monitor_release.yml

@@ -1,7 +1,7 @@
 name: monitor-release
 on:
   schedule:
-    - cron: "30 16 * * *"
+    - cron: "0 4 * * *"
   workflow_dispatch: {}
 jobs:
   monitor-release:

.github/workflows/monitor_sync.yml

@@ -0,0 +1,26 @@
+name: monitor-sync
+on:
+  schedule:
+    - cron: "0 22 * * *"
+  workflow_dispatch: {}
+jobs:
+  monitor-sync:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v4
+      - run: |
+          git fetch --prune --unshallow --tags
+          latest_commit=$(git log -1 --format="%at" | xargs -I{} date -d @{} "+%Y.%m.%d")
+          cur=$(date +"%Y.%m.%d")
+
+          if [ "$latest_commit" != "$cur" ]; then
+            >&2 echo "Warning: No repository sync for one or more days"
+            exit 101
+          fi
+          exit 0
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          REPOSITORY: ${{ github.repository }}
+          BRANCH_NAME: ${{ github.ref_name }}