Add meetup source to calendar event

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: HeyItsGilbert

content/calendar/meetup-315958850.md

@@ -1,5 +1,6 @@
 ---
 meetupEventId: "315958850"
+meetupSource: meetup
 startDate: "2026-09-09T17:30:00+02:00"
 endDate: "2026-09-09T19:30:00+02:00"
 title: "Swiss PSUG 09/2026"