Enable HTML validation in CI

Author: eXpl0it3r

.github/workflows/build.yml

@@ -1,4 +1,4 @@
-name: Build
+name: Build, Validate, Package & Publish
 
 on: [push, pull_request, workflow_dispatch]
 
@@ -82,3 +82,18 @@ jobs:
         foreach ($file in (Get-ChildItem ${{ env.NuGetDirectory }} -Recurse -Include *.*nupkg)) {
           dotnet nuget push $file --skip-duplicate --api-key ${{steps.login.outputs.NUGET_API_KEY}} --source https://api.nuget.org/v3/index.json
         }
+
+  validate:
+    name: Validate HTML and CSS
+    runs-on: ubuntu-24.04
+    steps:
+    - name: Checkout HTML Renderer
+      uses: actions/checkout@v6
+
+    - name: Validate HTML
+      uses: anishathalye/proof-html@v2
+      with:
+        directory: ./Source
+        check_html: true
+        check_css: true
+        ignore_missing_alt: true