🧪 [testing] Add coverage for run CLI arguments

[arvarik]

🎯 What: Added missing test coverage for gemstack run CLI arguments (--model, --max-cost, --max-tokens).
📊 Coverage: Verified that CLI options are correctly parsed and passed to the StepExecutor constructor, including default values.
✨ Result: Improved test reliability for the autonomous execution pipeline.

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PR created automatically by Jules for task 4296865290392515119 started by @arvarik

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