Refactor seasonal plugin configurations to improve clarity and consistency

- Updated comments for clarity on enabling/disabling features across various seasonal scripts.
- Changed default value checks to ensure undefined values are handled consistently.
- Enhanced readability by providing descriptive comments for configuration variables.

[skip ci]

Jellyfin.Plugin.Seasonals/Web/friday13.js

@@ -1,5 +1,5 @@
 const config = window.SeasonalsPluginConfig?.Friday13 || {};
-const friday13 = config.EnableFriday13 !== undefined ? config.EnableFriday13 : true;
+const friday13 = config.EnableFriday13 !== undefined ? config.EnableFriday13 : true; // enable/disable friday13
 
 let msgPrinted = false;