fix: Re-enable ticket-selection Stimulus controller registration

- Uncomment ticket-selection controller registration in JavaScript index
- Ensure ticket selection functionality works properly on event pages
- Fix controller not being available for ticket quantity management
- Required for proper cart functionality and checkout flow

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

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

app/javascript/controllers/index.js

@@ -14,7 +14,7 @@ import FlashMessageController from "./flash_message_controller";
 application.register("flash-message", FlashMessageController);
 
 import TicketSelectionController from "./ticket_selection_controller";
-// application.register("ticket-selection", TicketSelectionController);
+application.register("ticket-selection", TicketSelectionController);
 
 import HeaderController from "./header_controller";
 application.register("header", HeaderController);