Robot: Teensy 3.6 with the old robot's servo wiring and calibration

- LEGACY/Hexapod_Teensy/: old robot sketch (reference only).
- platformio.ini: robot env targets teensy36 (owner-confirmed board).
- Config.h: per-servo SERVOS table (pin, pulse at 0 deg, signed
  us/deg, pulse limits) built from the old sketch's pins, ranges, trims
  and the old Unity servo directions. Rear-left/front-left coxa offsets
  set to 0: the owner re-horns those two servos (the old +-90 left them
  at the end of travel; the sim showed them clamping).
- ServoDriver: 18 servos on hardware PWM (50 Hz, 16-bit); the Teensy 3.6
  Servo library stops at 12.
- Radio on CE 39 / CSN 15 with SPI SCK on pin 14.
- sim: analogWrite/PWM shims, pulses decoded through SERVOS (API v6).
- Docs: CLAUDE.md, READMEs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2026-current/sim/shim/Arduino.h

@@ -28,6 +28,18 @@ constexpr typename std::common_type<A, B>::type max(A a, B b) { return a > b ? a
 inline double radians(double deg) { return deg * (PI / 180.0); }
 inline double degrees(double rad) { return rad * (180.0 / PI); }
 
+// Pins and hardware PWM. analogWrite() pulses are recorded per pin, so the
+// simulation sees servo pulses exactly as the PWM hardware would make them.
+#define INPUT 0
+#define OUTPUT 1
+#define LOW 0
+#define HIGH 1
+void pinMode(uint8_t pin, uint8_t mode);
+void digitalWrite(uint8_t pin, uint8_t value);
+void analogWrite(uint8_t pin, int value);
+uint32_t analogWriteResolution(uint32_t bits);   // returns the previous resolution, like Teensyduino
+void analogWriteFrequency(uint8_t pin, float hz);
+
 // Simulated clock, advanced by the simulation (see SimHardware.cpp).
 uint32_t millis();
 uint32_t micros();

2026-current/sim/shim/SPI.h

@@ -1,2 +1,12 @@
 #pragma once
-// Nothing needed: the simulated RF24 doesn't talk SPI.
+#include <Arduino.h>
+
+// The simulated RF24 doesn't talk SPI; this only has to accept the pin setup.
+class SPIClass {
+public:
+  void begin() {}
+  void setSCK(uint8_t) {}
+  void setMOSI(uint8_t) {}
+  void setMISO(uint8_t) {}
+};
+extern SPIClass SPI;