Gate test execution with Test Set pre-requisites

Some tests only make sense to run after a setup or sanity check has passed. Test Sets now know that.

• Define a prerequisite test case for any Test Set.
• Dependent test cases only run when the prerequisite passes.
• Automatic gating: Thunders gates execution based on the prerequisite result. No manual intervention.

Use this for login flows, environment health checks, or any setup step that must succeed before the rest of the suite makes sense to run.

#Sprint26