fix: Correct ticket creation flow and home page availability check

- Fix incorrect route helper in tickets controller (order_checkout_path -> checkout_order_path)
- Add missing set_event before_action for create action
- Fix home page availability check to use ticket_types.available_quantity instead of tickets.quantity
- Update AGENT.md with ast-grep documentation for development tools

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

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

app/controllers/tickets_controller.rb

@@ -4,7 +4,7 @@
 # complete their details and proceed to payment
 class TicketsController < ApplicationController
   before_action :authenticate_user!, only: [ :new, :payment_success, :payment_cancel ]
-  before_action :set_event, only: [ :new ]
+  before_action :set_event, only: [ :new, :create ]
 
   # Handle new ticket creation
   #
@@ -87,7 +87,7 @@ class TicketsController < ApplicationController
     if success
       session[:draft_order_id] = @order.id
       session.delete(:pending_cart)
-      redirect_to order_checkout_path(@order)
+      redirect_to checkout_order_path(@order)
     else
       redirect_to ticket_new_path(@event.slug, @event.id)
     end