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/controllers/events_controller.rb

@@ -1,28 +1,35 @@
-# Events controller
+# Events controller - Public event listings and individual event display
 #
-# This controller manages all events. It load events for homepage
-# and display for pagination.
+# This controller manages public event browsing and displays individual events
+# with their associated ticket types. No authentication required for public browsing.
 class EventsController < ApplicationController
+  # No authentication required for public event viewing
   before_action :authenticate_user!, only: []
   before_action :set_event, only: [ :show ]
 
-  # Display all events
+  # Display paginated list of upcoming published events
+  #
+  # Shows events in published state, ordered by start time ascending
+  # Includes event owner information and supports Kaminari pagination
   def index
     @events = Event.includes(:user).upcoming.page(params[:page]).per(12)
   end
 
-  # Display desired event
+  # Display individual event with ticket type information
   #
-  # Find requested event and display it to the user
+  # Shows complete event details including venue information,
+  # available ticket types, and allows users to add tickets to cart
   def show
-    # Event is set by set_event callback
+    # Event is set by set_event callback with ticket types preloaded
+    # Template will display event details and ticket selection interface
   end
 
   private
 
-  # Set the current event in the controller
+  # Find and set the current event with eager-loaded associations
   #
-  # Expose the current @event property to method
+  # Loads event with ticket types to avoid N+1 queries
+  # Raises ActiveRecord::RecordNotFound if event doesn't exist
   def set_event
     @event = Event.includes(:ticket_types).find(params[:id])
   end