Add holiday management functionality with CRUD operations

- Implement HolidaysController for managing holidays
- Create Holiday model with validation for recurrence types
- Add holiday form and views for creating, editing, and listing holidays
- Integrate holiday checks into customer appointment scheduling
- Update locale file for holiday-related labels and error messages
- Add migration for holidays table
- Update plugin version and add holidays to admin menu

init.rb

@@ -14,12 +14,15 @@ Redmine::Plugin.register :redmine_qbo_calendar do
   name 'Redmine QBO Calendar plugin'
   author 'Rick Barrette'
   description 'A plugin for Redmine to extend the capabilitys of the Redmine QuickBooks Online plugin to create customer appointments for the Redmine Calendar'
-  version '2026.8.1'
+  version '2026.9.0'
   url 'https://github.com/rickbarrette/redmine_qbo_calendar'
   author_url 'https://barrettefabrication.com'
   requires_redmine version_or_higher: '7.0.0'
   settings partial: 'calendar/settings'
 
+  # Add Holidays index to the Redmine Administration Menu
+  menu :admin_menu, :holidays, { controller: 'holidays', action: 'index' }, caption: :label_holiday_plural, html: { class: 'icon icon-list' }
+
   # Ensure redmine_qbo is installed
   begin
     requires_redmine_plugin :redmine_qbo, version_or_higher: '2026.8.2'