e2e: block preview transaction when fee rate is invalid

[NishDs-06]

What kind of change does this PR introduce?

Test improvement / E2E test coverage

Issue Number:

Fixes subtask of #442

Snapshots/Videos:

Not applicable (test-only change)

If relevant, did you update the documentation?

Not applicable

Summary

This PR adds an end-to-end test to ensure that the Preview Transaction step
is not accessible when the fee rate input is invalid.

The test asserts that the system does not expose a forbidden transition
in the Send flow, ensuring users cannot proceed to transaction preview
when required preconditions are not met.

Does this PR introduce a breaking change?

No

Checklist

• I have tested my changes thoroughly.
• I have added or updated tests to cover my changes (if applicable).
• I have verified that test coverage meets or exceeds 95% (if applicable).
• I have run the test suite locally, and all tests pass.
• I have written tests for all new changes/features
• I have followed the project's coding style and conventions.
• I have created a changeset to document my changes (npm run changeset)

Other information

This test validates UI-level state transitions and remains valid even if
backend fee validation logic is refactored, as long as invalid fees must
not allow progression to the Preview step.

Have you read the contributing guide?

Yes

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Latest commit: af49a70

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Project	Deployment	Actions	Updated (UTC)
caravan-coordinator	Ready	Preview, Comment	Feb 9, 2026 7:33am