Run schema validation on all branches and PRs to main

Split workflow into validate and deploy jobs so validation
runs on every push and PR, while deployment only happens
on pushes to main.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: stefanhuber

.github/workflows/pages.yml

@@ -2,14 +2,28 @@ name: Deploy to GitHub Pages
 
 on:
   push:
+  pull_request:
     branches: [main]
 
 permissions:
   pages: write
   id-token: write
 
 jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: pip install check-jsonschema
+
+      - name: Validate examples
+        run: check-jsonschema --schemafile schema.json examples/*/data.json
+
   deploy:
+    if: github.ref == 'refs/heads/main' && github.event_name == 'push'
+    needs: validate
     runs-on: ubuntu-latest
     environment:
       name: github-pages
@@ -18,10 +32,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install dependencies
-        run: pip install json-schema-for-humans check-jsonschema
-
-      - name: Validate examples
-        run: check-jsonschema --schemafile schema.json examples/*/data.json
+        run: pip install json-schema-for-humans
 
       - name: Build site
         run: |