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/build.ps1

@@ -0,0 +1,42 @@
+# Builds the firmware simulation DLL and runs the headless smoke test.
+# Windows PowerShell 5.1 compatible. From the repo root:
+#
+#   .\sim\build.ps1             configure (first time) + build + smoke test
+#   .\sim\build.ps1 -NoTest     build only
+#   .\sim\build.ps1 -Clean      wipe sim\build first
+#
+# Output: sim\build\hexapod_sim.dll (loaded by the Unity project) and
+# sim\build\sim_smoke.exe. Exit code = build failure (1) or failed checks.
+param(
+    [switch]$NoTest,
+    [switch]$Clean
+)
+$ErrorActionPreference = 'Stop'
+
+$simDir = $PSScriptRoot
+$buildDir = Join-Path $simDir 'build'
+
+# g++/cmake/ninja: use what's on PATH, else Strawberry Perl's bundled toolchain.
+if (-not (Get-Command cmake -ErrorAction SilentlyContinue) -or -not (Get-Command g++ -ErrorAction SilentlyContinue)) {
+    $strawberry = 'C:\Strawberry\c\bin'
+    if (Test-Path $strawberry) {
+        $env:PATH = "$strawberry;$env:PATH"
+    } else {
+        Write-Error 'cmake and g++ not found. Install Strawberry Perl (bundles g++, cmake, ninja) or add a MinGW-w64 toolchain to PATH.'
+    }
+}
+
+if ($Clean -and (Test-Path $buildDir)) { Remove-Item $buildDir -Recurse -Force }
+
+if (-not (Test-Path (Join-Path $buildDir 'build.ninja'))) {
+    cmake -S $simDir -B $buildDir -G Ninja -DCMAKE_BUILD_TYPE=Release
+    if ($LASTEXITCODE -ne 0) { exit 1 }
+}
+
+cmake --build $buildDir
+if ($LASTEXITCODE -ne 0) { exit 1 }
+
+if (-not $NoTest) {
+    & (Join-Path $buildDir 'sim_smoke.exe')
+    exit $LASTEXITCODE
+}