feat: Implement comprehensive email notifications system

This commit implements a complete email notifications system for purchase
confirmations and event reminders as requested in the medium priority
backlog tasks.

## Features Added

### Purchase Confirmation Emails
- Automatically sent when orders are marked as paid
- Supports both single tickets and multi-ticket orders
- Includes PDF ticket attachments
- Professional HTML and text templates in French

### Event Reminder Emails
- Automated reminders sent 7 days, 1 day, and day of events
- Only sent to users with active tickets
- Smart messaging based on time until event
- Venue details and ticket information included

### Background Jobs
- EventReminderJob: Sends reminders to all users for a specific event
- EventReminderSchedulerJob: Daily scheduler to queue reminder jobs
- Proper error handling and logging

### Email Templates
- Responsive HTML templates with ApéroNight branding
- Text fallbacks for better email client compatibility
- Dynamic content based on number of tickets and time until event

### Configuration & Testing
- Environment-based SMTP configuration for production
- Development setup with MailCatcher support
- Comprehensive test suite with mocking for PDF generation
- Integration tests for end-to-end functionality
- Documentation with usage examples

## Technical Implementation
- Enhanced TicketMailer with new notification methods
- Background job scheduling via Rails initializer
- Order model integration for automatic purchase confirmations
- Proper associations handling for user/ticket relationships
- Configurable via environment variables

## Files Added/Modified
- Enhanced app/mailers/ticket_mailer.rb with order support
- Added app/jobs/event_reminder_*.rb for background processing
- Updated email templates in app/views/ticket_mailer/
- Added automatic scheduling in config/initializers/
- Comprehensive test coverage in test/ directory
- Complete documentation in docs/email-notifications.md

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

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

app/jobs/event_reminder_job.rb

@@ -0,0 +1,19 @@
+class EventReminderJob < ApplicationJob
+  queue_as :default
+
+  def perform(event_id, days_before)
+    event = Event.find(event_id)
+    
+    # Find all users with active tickets for this event
+    users_with_tickets = User.joins(orders: { tickets: :ticket_type })
+                            .where(ticket_types: { event: event })
+                            .where(tickets: { status: "active" })
+                            .distinct
+
+    users_with_tickets.find_each do |user|
+      TicketMailer.event_reminder(user, event, days_before).deliver_now
+    rescue StandardError => e
+      Rails.logger.error "Failed to send event reminder to user #{user.id} for event #{event.id}: #{e.message}"
+    end
+  end
+end