[FR] Scissor-lift Z kinematic

### Description

My Z steps per mm need to be proportional to the position (like a Scissor Lift) I may have made an altogether new type of kinematics ( Cartesian with a twist). I am not very good at writing code more of a moron still sending morose code through my telegraph. lol.

I'm sure its a simple couple lines of code to calculate the Z motor travel with the actual bed displacement the math is easy enough thanks to the Pythagorean theorem

The issue names no files, tests, or entry points. Start by locating Marlin's Z steps-per-mm handling and existing kinematics implementations, then determine how scissor-lift geometry would fit the firmware's motion model. Done means supporting position-dependent Z motor travel for the described bed displacement while preserving existing Cartesian behavior.

Written by the indexing model from the issue text.