Add scheduled build to Hugo workflow

Introduces a cron schedule to the GitHub Actions workflow for Hugo, triggering a build and deploy every day at midnight in addition to builds on push to main.

.github/workflows/hugo.yml

@@ -1,5 +1,7 @@
 name: Build and deploy
 on:
+  schedule:
+    - cron: "0 0 * * *"
   push:
     branches:
       - main