feat: Add booking control during events

- Add allow_booking_during_event boolean field to events (defaults to false)
- Implement booking_allowed? method to check if tickets can be purchased
- Add event_started? and event_ended? helper methods
- Include new option in event edit form with clear explanation
- Display booking policy status on event show page
- Add visual indicator when booking is disabled during ongoing events
- Update controller to permit new parameter

This allows promoters to control whether attendees can purchase tickets
after an event has started, providing flexibility for different event types.

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

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

app/controllers/promoter/events_controller.rb

@@ -111,7 +111,7 @@ class Promoter::EventsController < ApplicationController
     params.require(:event).permit(
       :name, :slug, :description, :image,
       :venue_name, :venue_address, :latitude, :longitude,
-      :start_time, :end_time, :featured
+      :start_time, :end_time, :featured, :allow_booking_during_event
     )
   end
 end