feat(ci): add org-default markdownlint config with workflow fallback

.github/workflows/_markdown-lint.yml

@@ -1,5 +1,5 @@
 # Reusable: Markdown Lint
-# Generic markdown linting — uses the calling repo's own markdownlint config.
+# Uses the calling repo's own markdownlint config, falling back to org defaults.
 name: _markdown-lint
 
 on:
@@ -20,6 +20,13 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v6
 
+      - name: Apply org-default markdownlint config
+        if: hashFiles('.markdownlint-cli2.jsonc', '.markdownlint-cli2.yaml', '.markdownlint-cli2.cjs', '.markdownlint-cli2.mjs', '.markdownlint.jsonc', '.markdownlint.json', '.markdownlint.yaml', '.markdownlint.yml', '.markdownlint.cjs', '.markdownlint.mjs') == ''
+        run: |
+          curl -sSfL --retry 3 --retry-connrefused \
+            "https://raw.githubusercontent.com/${{ github.repository_owner }}/.github/main/configs/.markdownlint-cli2.yaml" \
+            -o .markdownlint-cli2.yaml
+
       - name: Run markdownlint
         uses: DavidAnson/markdownlint-cli2-action@v22
         with:

configs/.markdownlint-cli2.yaml

@@ -0,0 +1,22 @@
+# Organization-wide markdownlint defaults
+# Repos inherit this via the _markdown-lint.yml reusable workflow.
+# To override: add a .markdownlint-cli2.yaml to your repo root.
+config:
+  MD013:
+    line_length: 160
+    heading_line_length: 80
+    code_block_line_length: 80
+    tables: true
+    strict: true
+
+  # Allow duplicate headings in different sections (standard for changelogs)
+  MD024:
+    siblings_only: true
+
+# Per-file overrides
+overrides:
+  - files:
+      - "CHANGELOG.md"
+    config:
+      # release-please generates long lines with PR links
+      MD013: false