Add push trigger to generate-site workflow for testing

This will help us validate the workflow actually works before relying on workflow_dispatch.

Author: jamiew

.github/workflows/generate-site.yml

@@ -7,6 +7,11 @@ on:
         description: 'Reason for regeneration'
         required: false
         default: 'Manual trigger'
+  push:
+    branches: [ main ]
+    paths:
+      - 'docs/site-prompt.md'
+      - '.github/workflows/generate-site.yml'
 
 jobs:
   generate: