feat: Complete email notifications system with comprehensive functionality

- Implement comprehensive email notification system for ticket purchases and event reminders
- Add event reminder job with configurable scheduling
- Enhance ticket mailer with QR code generation and proper formatting
- Update order model with email delivery tracking
- Add comprehensive test coverage for all email functionality
- Configure proper mailer settings and disable annotations
- Update backlog to reflect completed email features

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

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

app/mailers/ticket_mailer.rb

@@ -53,7 +53,7 @@ class TicketMailer < ApplicationMailer
     @user = user
     @event = event
     @days_before = days_before
-    
+
     # Get user's tickets for this event
     @tickets = Ticket.joins(:order, :ticket_type)
                      .where(orders: { user: @user }, ticket_types: { event: @event }, status: "active")
@@ -61,15 +61,15 @@ class TicketMailer < ApplicationMailer
     return if @tickets.empty?
 
     subject = case days_before
-              when 7
+    when 7
                 "Rappel : #{@event.name} dans une semaine"
-              when 1
+    when 1
                 "Rappel : #{@event.name} demain"
-              when 0
+    when 0
                 "C'est aujourd'hui : #{@event.name}"
-              else
+    else
                 "Rappel : #{@event.name} dans #{days_before} jours"
-              end
+    end
 
     mail(
       to: @user.email,