Add example YAML event configuration and update .gitignore

- Introduce `event.yml.example` providing a template for event-level configuration.
- Extend `.gitignore` to include `event.yml` to prevent committing real event data.

.gitignore

@@ -14,6 +14,9 @@
 # Real participant data (copy to "Export Brevetkarte.csv" and fill in)
 Export Brevetkarte.csv
 
+# Real event data (copy event.yml.example to event.yml and fill in)
+event.yml
+
 # Generated files
 brevetkarte-personalized.tex