[Contracts] Implement Keep-Alive Ping Ledger Updates

[ONEONUORA]

Description

Write the ping entrypoint:

• Checks if the caller is the plan owner (auth check).
• Resets last_ping field to the current ledger timestamp.
• Bump storage TTL for the plan.

Acceptance Criteria

• Rejects calls from addresses other than the owner.
• Successfully updates last_ping.
• Emits a contract event detailing the keep-alive ping.

[spiffamani]

@spiffamani has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hey,

I'm a full-stack Software Engineer with 3 years of experience and a background in Blockchain development. I'm relatively new to open-source but I pick things up fast and I'm genuinely interested in this issue.
My main stack is React, TypeScript and Next.js on the frontend — I focus on clean component architecture, responsive design and performance. On the backend I work with Node.js, Java and Rust, handling everything from API design to database modeling.
A few things I've built:

https://www.zendvo.com/
https://cleanrest.vercel.app/

I'm comfortable jumping into an existing codebase, following conventions and shipping clean, maintainable code. My GitHub shows the kind of work I do better than I can describe it.
I'd love to take this on — thanks for considering me.

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

[drips-wave]

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

🧑‍💻 @ejioforJs: 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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[ONEONUORA]

@ejioforJs
Pls update on this issue
You will be unassign in 6 hours

[Meme11030]

@Meme11030 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi maintainer I will like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Meme11030 to this issue.

[fairbid01]

@fairbid01 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

GM, I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @fairbid01 to this issue.

[Kappa16]

@Kappa16 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Please maintainer..I can handle this professionally and make sure this issue is closed ASAP WITHOUT ERRORS.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Kappa16 to this issue.