Write unit tests for `StellarWalletProvider` wallet creation and restoration

[Emmzyemms]

Description:
StellarWalletProvider handles embedded wallet creation, encrypted storage, and restoration — critical security-sensitive logic with no test coverage.

Acceptance Criteria:

• Tests cover: wallet creation on first load, wallet restoration from encrypted storage, failed decryption handling, wallet export (public key only)
• secureStorage is mocked to isolate the provider logic
• Tests are in __tests__/components/StellarWalletProvider.test.tsx
• Edge cases: corrupted storage data, missing salt, concurrent mount calls

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[fridaypetra55-afk]

@fridaypetra55-afk has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I have reviewed the issue requirements and would love to contribute. I am comfortable working with smart contracts, backend systems, and developer tooling. I will provide regular updates and ensure high-quality implementation.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @fridaypetra55-afk to this issue.

[drips-wave]

Congratulations, @fridaypetra55-afk! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @fridaypetra55-afk: 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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