[CT-12] Implement ticket cancellation with refund

[yusuftomilola]

Overview

Allow ticket holders (or admin) to cancel a ticket and receive a full refund before the event starts. Work inside contracts/sandbox/event_ticketing/.

Acceptance Criteria

• cancel_ticket(env, caller, ticket_id) is implemented
• Only ticket owner or admin may cancel
• Returns Error::TicketNotFound if ticket doesn't exist
• Cannot cancel after event start time (returns appropriate error)
• Refunds ticket_price from contract to ticket owner
• Sets ticket status to Cancelled
• Restores one unit of event capacity
• Emits a cancellation event
• Code compiles with cargo build

[JoeX17]

@JoeX17 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

can i work on this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @JoeX17 to this issue.

[drips-wave]

Congratulations, @JoeX17! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @JoeX17: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @JoeX17 as part of the Stellar Wave Program's 4th Wave 🥳

😎 @JoeX17: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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