Add note backup confirmation gate before pool deposit

[collinsadi]

Losing the withdrawal note after a deposit means permanently losing the funds, and nothing currently forces users to secure it first.

Require an explicit note backup step, with verification, before the deposit transaction can be signed.

Acceptance criteria:

• Deposit signing is blocked until backup is confirmed.
• Verification requires re-entering or re-selecting a note fragment.
• The gate cannot be bypassed by page reload mid-flow.

[dev-shierly]

@dev-shierly has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi maintainer! I would love to help you with this issue. Given my theoretical knowledge and background, I am quite sure that I am well-equipped to tackle it. Please kindly assign it to me.

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

[overprodigy]

@overprodigy has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I can take this on. I've gone through the details and will provide a well-tested solution aligned with the project standards.

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

[drips-wave]

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

🧑‍💻 @overprodigy: 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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