test: cover StreamCreationWizard flow and txHash propagation

[afeezorobsco-cyber]

##close #1284

Summary

Add test coverage for the StreamCreationWizard's primary conversion flow and fix the txHash propagation bug identified during the second-wave repository audit.

What changed

• Added coverage for per-step validation and progression gating.
• Added coverage for the submit → poll → redirect flow using mocked indexer responses.
• Added coverage for the startPolling timeout path.
• Added coverage for loading, success, and failure states.
• Added a regression test verifying that the txHash returned by onSubmit is propagated and surfaced correctly.
• Fixed the underlying txHash propagation issue exposed by the regression test.
• Kept network/indexer interactions mocked and deterministic.

Regression coverage

The new txHash test asserts that a concrete txHash returned by onSubmit is available to the resulting UI/state rather than becoming undefined.

This test would fail against the previous implementation and passes with the fix.

Testing

Ran:

npm test
npm run typecheck
npm run lint

Closes #[ISSUE_NUMBER]