[Contract] Add top-level docs to lib.rs

[Yunusabdul38]

Description: Improve project documentation by adding module-level doc comments to the main lib.rs file, providing a high-level overview of the contract architecture. Tasks:

Add //! comments to the top of lib.rs.
Include sections on Overview, Architecture, and Usage.
Explain how EventRegistry interacts with TicketPayment.

[Coredevjay]

@Coredevjay has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

i can work on this , can you assign this to me?

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

[Johnsmichael150]

@Johnsmichael150 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi maintainer, I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Johnsmichael150 to this issue.

[drips-wave]

Congratulations, @Coredevjay! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @Coredevjay: 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.

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🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @Coredevjay as part of the Stellar Wave Program's 3rd Wave 🥳

😎 @Coredevjay: 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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