Add 4 TDD tests for the var-vs-var comparison feature (S1-TT2): - test_cmd_if_var_vs_var_eq - test_cmd_if_var_vs_var_ne - test_cmd_if_var_vs_var_contains - test_cmd_if_var_vs_var_not_contains All tests fail because the grammar only accepts SIMPLEVALUE on RHS, not IDENTIFIER. Implementation in S1-T2 will make them pass.