ci: enforce markdownlint on all markdown

.github/workflows/lint.yml

@@ -23,3 +23,13 @@ jobs:
         with:
           version: "0.15.18"
           args: "format --check"
+
+  markdownlint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: markdownlint
+        uses: DavidAnson/markdownlint-cli2-action@v20
+        with:
+          globs: "**/*.md"

.markdownlint-cli2.yaml

@@ -0,0 +1,16 @@
+# markdownlint-cli2 configuration — see https://github.com/DavidAnson/markdownlint
+config:
+  MD013: false # line length (tables, code and long prose)
+  MD033: false # inline HTML (badges, <img>)
+  MD041: false # first line need not be a top-level heading (badges)
+  MD024:
+    siblings_only: true # repeated headings OK across different sections
+  MD046: false # allow both indented and fenced code blocks
+  MD060: false # don't enforce table pipe spacing style
+globs:
+  - "**/*.md"
+ignores:
+  - "site"
+  - ".pixi"
+  - "PUBLIC"
+  - "**/node_modules"