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/views/pages/home.html.erb

@@ -36,7 +36,7 @@
               <% if event.featured? %>
                 <span class="badge badge-featured">★ En vedette</span>
               <% end %>
-              <% if event.tickets.any? { |ticket| ticket.quantity > 0 } %>
+              <% if event.ticket_types.any? { |ticket_type| ticket_type.available_quantity > 0 } %>
                 <span class="badge badge-available">Disponible</span>
               <% end %>
             </div>