[S4] Add a useXdrTransaction hook to centralise sign-and-submit logic

[Akshola00]

Description

Pool creation and donation both follow the same XDR round-trip pattern:

1. Call API to get unsigned XDR
2. Ask Freighter to sign it
3. Submit signed XDR back to the API
4. Show pending → success / error state

Without a shared hook this state logic will be copy-pasted into both pools/new/page.tsx and DonateModal.tsx, making it hard to fix consistently.

Deliverables

• Create nevo_frontend/hooks/useXdrTransaction.ts that exposes:

  const { submit, status, txHash, error } = useXdrTransaction()
  // status: 'idle' | 'signing' | 'submitting' | 'success' | 'error'

• submit(getXdr: () => Promise<string>, submitXdr: (signed: string) => Promise<string>) handles the full flow
• Hook calls Freighter's signTransaction internally (from lib/stellar.ts)
• Returns txHash on success, error string on failure
• npm run build passes with the hook in place (even if not yet wired to forms)

Notes

Depends on: #721 (XDR signing step for pool creation), #726 (donate function in API client)

[OtowoSamuel]

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

I would love to work on this!

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

[drips-wave]

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

🧑‍💻 @OtowoSamuel: 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

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @OtowoSamuel as part of the Stellar Wave Program's 6th Wave 🥳

😎 @OtowoSamuel: 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.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.