ci: 中央テンプレの markdown-lint caller を導入する

.github/dependabot.yml

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+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 5

.github/workflows/md-lint.yml

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+name: Markdown Lint
+
+# tomio2480/github-workflows v2 の composite action を呼び出す caller workflow．
+# 参照は @<SHA> # <version> 形式の SHA pin で，Dependabot が更新 PR を起票する．
+# 設定の上書きが必要な場合はリポジトリルートに以下のいずれかを置けば優先される：
+#   .markdownlint-cli2.yaml / .textlintrc.json / prh.yml / .textlintignore
+# 詳細は https://github.com/tomio2480/github-workflows の README を参照．
+
+on:
+  pull_request:
+    paths:
+      - "**/*.md"
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  lint:
+    name: Markdown Lint
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      - name: Markdown Lint via composite action
+        uses: tomio2480/github-workflows/.github/actions/markdown-lint@20a93b5ca42235c26c13e742ccfcdee2ac999b99 # v2.6.0
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}