Add weekly scheduled rebuild to pages workflow (#75)

Rebuilds the site every Wednesday at noon UTC so that past events
are no longer displayed as upcoming after Tuesday Hacknight nights.

Fixes the root cause: Jekyll bakes event dates into static HTML at
build time; without a scheduled trigger, stale 'upcoming' events
persist indefinitely until a push or manual dispatch occurs.

Author: alexwolson

.github/workflows/pages.yml

@@ -6,6 +6,8 @@ on:
       - main # Adjust if your default branch is different
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:
+  schedule:
+    - cron: '0 12 * * 3'  # Every Wednesday at noon UTC (after Tuesday Hacknight events)
 
 # Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages
 permissions: