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/sim/shim/EEPROM.h

@@ -0,0 +1,17 @@
+#pragma once
+// Not used by robot/ today; here so a future robot-side EEPROM use doesn't
+// break the simulation build silently. Backed by RAM, starts erased (0xFF).
+#include <Arduino.h>
+
+class SimEEPROM {
+public:
+  template <class T> T& get(int addr, T& t) { memcpy(&t, mem_ + addr, sizeof(T)); return t; }
+  template <class T> const T& put(int addr, const T& t) { memcpy(mem_ + addr, &t, sizeof(T)); return t; }
+  uint8_t read(int addr) { return mem_[addr]; }
+  void write(int addr, uint8_t v) { mem_[addr] = v; }
+  SimEEPROM() { memset(mem_, 0xFF, sizeof(mem_)); }
+
+private:
+  uint8_t mem_[4284];
+};
+extern SimEEPROM EEPROM;