chore: add markdown linting config and CI workflow

.github/workflows/lint.yml

@@ -0,0 +1,19 @@
+name: Lint
+
+on:
+  pull_request:
+    paths:
+      - '**/*.md'
+      - '.markdownlint-cli2.jsonc'
+
+jobs:
+  markdown:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+      - run: npm ci
+      - run: npm run lint:md

.markdownlint-cli2.jsonc

@@ -0,0 +1,10 @@
+{
+  // Only enforce the 3 rules from PR #72. Everything else is off.
+  "config": {
+    "default": false,
+    "MD012": true,
+    "MD022": true,
+    "MD032": true
+  },
+  "ignores": ["node_modules/**", "dist/**", "src-tauri/target/**"]
+}