Firmware simulation, Unity project, and sim-verified robot fixes

Simulation
- sim/: the unchanged robot firmware compiled into hexapod_sim.dll
  against PC stand-ins (Arduino, Servo, Wire + register-level MPU6050,
  RF24 with matching-config radio), a kinematic body model (support
  plane + planted-foot odometry) that also drives the simulated IMU,
  and a headless smoke test (sim_smoke). build.ps1 builds and tests.
- Hexapod_Simulation_Unity/ folded in (history kept in a bundle
  outside the repo). Assets/HexapodSim loads the DLL, drives the
  existing leg rig, and offers joystick / keyboard / robot-serial
  input plus a test panel.

Robot (all found or confirmed in the simulation)
- Config.h geometry taken from the Unity model.
- IK femur elevation sign, gait stance direction, body pose
  rotation direction, yaw lever arm.
- Stance feet integrated from the current command; gait restarts at
  mid-stance; heading integrates the applied turn rate, only while
  walking.
- Leg clearance and reach checks (Limits::feetFeasible); walk command
  and body pose scaled as a whole, pose scale rate-limited, planted
  feet guarded so the body never snaps or legs collide.
- Robot-gyro self-leveling as an integrator.
- Heading mode: steering relative to the body; S walks backward.
- Standing height from the remote (STANCE_HEIGHT_RANGE_MM).

Protocol v3 (reflash both boards)
- CmdPacket gains body_height (22 bytes).

Remote
- Height slider (Nextion hHeight/nHeight, serial [ ]).
- Fixed unspecified I2C read order in RemoteIMU.

LEGACY/: owner's old Nextion HMI and remote hardware assets.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2026-current/robot/Kinematics.h

@@ -17,6 +17,17 @@ public:
   // Solves leg i's joint angles for a body-frame foot target.
   static JointAngles solve(int leg_index, const FootTarget& target);
 
-  // The leg's resting/neutral foot target, in body frame.
+  // The leg's resting/neutral foot target, in body frame, at the current
+  // stance height.
   static FootTarget neutralStance(int leg_index);
+
+  // Standing height: how far below the hips the neutral feet sit (starts at
+  // STANCE_HEIGHT_MM). Everything built on neutralStance() - gait, sit/stand,
+  // workspace limits - follows it.
+  static void setStanceHeight(float mm);
+  static float stanceHeight();
+
+  // Forward kinematics: the leg's joint positions for the given angles, body
+  // frame - [0] coxa pivot (hip), [1] femur pivot, [2] knee, [3] foot.
+  static void jointPositions(int leg_index, const JointAngles& a, FootTarget out[4]);
 };