fix(cards): add default SVar:X:1 for Clay Golem monstrosity roll

[steple]

Summary

Fixes an issue with Clay Golem where calculating the monstrosity counter amount before or outside of dynamic dice resolution could fail or misbehave due to a missing fallback definition for variable X.

Details

• Added SVar:X:1 to clay_golem.txt.
• When rolling for monstrosity (RollDice<1/8/X>), X is determined dynamically during activation/resolution, but having a default value (SVar:X:1) ensures AbilityUtils.calculateAmount and any static/AI evaluations evaluate safely to a valid base value instead of evaluating an undefined variable.
• Added a unit test (ClayGolemTest) verifying that Clay Golem loads with default SVar:X=1, retains its Monstrosity X ability parameter, and correctly calculates the amount.

Gemini contributed.

[tool4ever]

• don't need tests for trivial stuff
• we need a generic helper to perform cost lookahead, see Let the AI count converge before it decides whether to cast #11486 (comment)
• you could just fix the AILogic$ branch instead