Add HTML linting CI (html-validate) and config

.github/workflows/html-lint.yml

@@ -0,0 +1,21 @@
+name: HTML Lint
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  html-lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '18'
+      - name: Install dependencies
+        run: npm ci
+      - name: Run html-validate
+        run: npx html-validate "**/*.html"

.htmlvalidate.json

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+{
+  "extends": ["html-validate:recommended"],
+  "rules": {
+    "attr-no-dup": "error",
+    "doctype-style": "error",
+    "element-no-empty": ["warn", {"void": true}]
+  }
+}

package.json

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+{
+  "name": "people-cost-counter",
+  "version": "0.0.0",
+  "private": true,
+  "devDependencies": {
+    "html-validate": "^8.8.0"
+  },
+  "scripts": {
+    "lint:html": "html-validate \"**/*.html\""
+  }
+}