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/RemoteState.cpp

@@ -56,6 +56,10 @@ bool RemoteState::handle(const UiEvent& e, Sticks& stick_hw, RemoteIMU& imu, uin
     case UiCmd::SpeedUp:   speed_target_ = (uint8_t)min(255, speed_target_ + SPEED_SCALE_STEP); return true;
     case UiCmd::SpeedDown: speed_target_ = (uint8_t)max(0, speed_target_ - SPEED_SCALE_STEP);   return true;
 
+    case UiCmd::SetHeight:  height_ = (int16_t)constrain(((int)e.value - 100) * 10, -1000, 1000); return true;
+    case UiCmd::HeightUp:   height_ = (int16_t)min(1000, height_ + HEIGHT_STEP);  return true;
+    case UiCmd::HeightDown: height_ = (int16_t)max(-1000, height_ - HEIGHT_STEP); return true;
+
     case UiCmd::ZeroGyro:
       imu.zeroLevel();
       setMessage("Remote level zeroed", now);
@@ -110,5 +114,6 @@ void RemoteState::fillView(UiView& v, uint32_t now_ms) const {
   v.robot_gyro = robot_gyro_;
   v.calibrating = calibrating_;
   v.speed_target = speed_target_;
+  v.height = height_;
   v.message = message(now_ms);
 }