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/NEXTION.md

@@ -1,5 +1,10 @@
 # Nextion HMI build guide
 
+> The owner's earlier 6-page HMI is in `LEGACY/remote/remote.HMI`. This
+> guide describes the minimal single page the current firmware expects.
+> To reuse the old HMI instead, `NextionUI` has to be changed to match
+> its component names.
+
 The firmware drives the display by **component name**, and the display
 talks back with small custom frames sent from each button's touch event.
 Build one page in Nextion Editor to match the tables below. Layout, fonts
@@ -40,6 +45,8 @@ the firmware writes. Button bounds here allow some slack.
 | `bBGyro` | Button  | –        | bco green / gray (label it "ROBOT GYRO")     |
 | `hSpeed` | Slider  | –        | `val` 0..255 (set **maxval = 255**)          |
 | `nSpeed` | Number  | –        | `val` 0..100 (speed %)                       |
+| `hHeight`| Slider  | –        | `val` 0..200, 100 = default (set **maxval = 200**) |
+| `nHeight`| Number  | –        | `val` -100..100 (height offset %)            |
 | `bCal`   | Button  | 9        | `CAL` / `SAVE CAL`, bco orange while active  |
 | `bCalX`  | Button  | –        | nothing (static "CANCEL CAL")                |
 | `bZero`  | Button  | –        | nothing (static "LEVEL")                     |
@@ -63,6 +70,7 @@ uses **Touch Move** as well so the value tracks your finger). Frame format:
 | `bRGyro`  | `printh 23 01 52`                        | `R` remote-gyro tilt on/off    |
 | `bBGyro`  | `printh 23 01 42`                        | `B` robot self-stabilize on/off |
 | `hSpeed`  | `printh 23 02 56`<br>`prints hSpeed.val,1` | `V` + speed byte             |
+| `hHeight` | `printh 23 02 48`<br>`prints hHeight.val,1` | `H` + height byte (Touch Move + Release) |
 | `bZero`   | `printh 23 01 5A`                        | `Z` zero handset level         |
 | `bCal`    | `printh 23 01 43`                        | `C` start / save stick calibration |
 | `bCalX`   | `printh 23 01 51`                        | `Q` cancel calibration         |