* M0: reject negative fractional GCD and LCM arguments
Validate the original input before truncation. Add scalar and range regressions, including signed zero, positive fractions and zero-first LCM validation.
* M0: document negative-fraction GCD and LCM regression
Record tested edge-case behavior and update the parity revision history. Function counts and readiness estimates remain unchanged.
* M0: preserve GCD and LCM regression after math test extraction
Move the original negative-fraction regression into the existing extracted math tests. Scalar and range cases, zero-first validation, signed zero and positive truncation coverage are unchanged.