test: add tests for submitTransaction and getTransactionStatus

[Trovic1]

Summary

Closes #249

Adds comprehensive test coverage for submitTransaction (src/transaction/submitTransaction.ts) and getTransactionStatus (src/transaction/status.ts) in a new file src/tests/transaction-submit-status.test.ts.

How the mocks work

• createHorizonServer from src/shared/serverFactory is mocked via �i.mock('../shared/serverFactory') returning a controlled object with submitTransaction and ransactions().transaction().call() fns — both are �i.fn() so each test can set its own resolved/rejected value without any network calls.
• TransactionBuilder.fromXDR is kept real for submitTransaction tests so the actual passphrase-mismatch detection logic runs against real signed XDRs.
• Hoisted helpers (mockSubmit, mockTransactionCall) are declared with �i.hoisted() so they are available before �i.mock is hoisted by Vitest.

Acceptance criteria coverage

submitTransaction

• ✅ Successful submission returns { status: 'success', hash }
• ✅ Horizon error returns TX_SUBMIT_FAILED
• ✅ Malformed XDR returns TX_SUBMIT_FAILED
• ✅ Network passphrase mismatch returns TX_SUBMIT_FAILED (caught client-side, Horizon never called)
• ✅ Cache is populated on success

getTransactionStatus

• ✅ x.successful === true maps to 'success'
• ✅ x.successful === false maps to 'failed'
• ✅ ledger_attr === 0 maps to 'pending' with no ledger number
• ✅ 404 returns TX_NOT_FOUND
• ✅ Other errors return TX_SUBMIT_FAILED
• ✅ Cache hit skips Horizon entirely
• ✅ Successful lookup is written to cache

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