test(cli): cover dataset name resolution branches

[plum2003]

Summary

• add focused unit coverage for DatasetService.resolve_dataset_name
• cover zero, one, and two template-prefix matches with a fake client
• verify the configured page size is forwarded to list_datasets
• leave production behavior unchanged

Validation

• targeted tests: 3 passed
• complete CLI tests: 59 passed
• type validation and pre-commit checks passed

Closes #259

[Copilot]

Pull request overview

Adds focused unit tests for DatasetService.resolve_dataset_name in the rosetta-cli to ensure the dataset auto-detection logic is exercised directly (rather than being monkeypatched away), aligning with the gap called out in #259.

Changes:

• Introduces a small FakeClient to drive deterministic list_datasets responses.
• Adds parametrized coverage for 0/1/2 template-prefix match outcomes, including the ambiguous-match failure path.
• Asserts the configured page_size is forwarded to the client’s list_datasets call.

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