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/remote/NextionUI.cpp

@@ -46,6 +46,7 @@ bool NextionUI::decodeCustom(UiEvent& out) {
     case 'R': out.cmd = UiCmd::ToggleRemoteGyro;  break;
     case 'B': out.cmd = UiCmd::ToggleRobotGyro;   break;
     case 'V': out.cmd = UiCmd::SetSpeed;          break;
+    case 'H': out.cmd = UiCmd::SetHeight;         break;
     case 'Z': out.cmd = UiCmd::ZeroGyro;          break;
     case 'C': out.cmd = UiCmd::CalStartSave;      break;
     case 'Q': out.cmd = UiCmd::CalCancel;         break;
@@ -124,6 +125,10 @@ void NextionUI::pushState(const UiView& v, bool full) {
     cmd("hSpeed.val=%u", v.speed_target);
     cmd("nSpeed.val=%u", (v.speed_target * 100 + 127) / 255);
   }
+  if (full || v.height != s.height) {
+    cmd("hHeight.val=%d", v.height / 10 + 100);   // slider 0..200, 100 = default
+    cmd("nHeight.val=%d", v.height / 10);         // -100..100 %
+  }
   if (full || v.calibrating != s.calibrating) {
     cmd("bCal.txt=\"%s\"", v.calibrating ? "SAVE CAL" : "CAL");
     cmd("bCal.bco=%u", v.calibrating ? COL_WARN : COL_OFF);