refactor(cli): complete remaining audit items — validate status, extract helpers...

refactor(cli): complete remaining audit items — validate status, extract helpers, add 8 test cases

- Fix #28: Validate ResponsePayload status is string before cast in handleMessage()
- Fix #43: Extract settleHandler() private method to reduce duplication
- Fix #41: Normalize createMockWS → createMockWs for consistency
- Fix #39: Extract captureStream() parameterized helper to replace captureStdout/captureStderr
- Fix #47: Filter empty arrays in displayGenericPayload to avoid spurious output
- Test #21-#22: Add ConnectionError edge cases (empty cause, non-Error cause)
- Test #23: Add ServerFailureError without hashIdsFailed
- Test #24: Add post-connect onerror rejection test
- Test #25: Add displayGenericPayload failure path test
- Test #26: Add NaN and Infinity timeout validation tests

All tests pass, zero lint warnings.