refactor: Improve code quality and add comprehensive documentation

- Remove unused create_stripe_session method from TicketsController
- Replace hardcoded API key with environment variable for security
- Fix typo in ApplicationHelper comment
- Improve User model validation constraints for better UX
- Add comprehensive YARD-style documentation across models, controllers, services, and helpers
- Enhance error handling in cleanup jobs with proper exception handling
- Suppress Prawn font warnings in PDF generator
- Update refactoring summary with complete change documentation

All tests pass (200 tests, 454 assertions, 0 failures)
RuboCop style issues resolved automatically

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/helpers/flash_messages_helper.rb

@@ -1,4 +1,16 @@
+# Flash messages helper for consistent styling across the application
+#
+# Provides standardized CSS classes and icons for different types of flash messages
+# using Tailwind CSS classes and Lucide icons for consistent UI presentation
 module FlashMessagesHelper
+  # Return appropriate Tailwind CSS classes for different flash message types
+  #
+  # @param type [String, Symbol] The flash message type (notice, error, warning, info)
+  # @return [String] Tailwind CSS classes for styling the flash message container
+  #
+  # Examples:
+  #   flash_class('success') # => "bg-green-50 text-green-800 border-green-200"
+  #   flash_class('error')   # => "bg-red-50 text-red-800 border-red-200"
   def flash_class(type)
     case type.to_s
     when "notice", "success"
@@ -14,6 +26,14 @@ module FlashMessagesHelper
     end
   end
 
+  # Return appropriate Lucide icon for different flash message types
+  #
+  # @param type [String, Symbol] The flash message type
+  # @return [String] HTML content tag with Lucide icon data attribute
+  #
+  # Examples:
+  #   flash_icon('success') # => <i data-lucide="check-circle" class="..."></i>
+  #   flash_icon('error')   # => <i data-lucide="x-circle" class="..."></i>
   def flash_icon(type)
     case type.to_s
     when "notice", "success"