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/SimHardware.cpp

@@ -4,6 +4,7 @@
 #include <Servo.h>
 #include <Wire.h>
 #include <RF24.h>
+#include <SPI.h>
 #include <EEPROM.h>
 #include <HexapodProtocol.h>
 #include <stdarg.h>
@@ -13,6 +14,7 @@
 
 SimSerial Serial;
 TwoWire Wire;
+SPIClass SPI;
 SimEEPROM EEPROM;
 
 // =====================================================================
@@ -103,6 +105,36 @@ void Servo::writeMicroseconds(int us) {
   g_pins[pin_].writes++;
 }
 
+// ---- Hardware PWM (how ServoDriver drives the servos on the Teensy 3.6) ----
+static uint32_t g_pwm_bits = 8;                 // Teensyduino default
+static float g_pwm_hz[simhw::MAX_PINS];         // 0 = not set (Teensy default ~488 Hz)
+
+void pinMode(uint8_t pin, uint8_t mode) {
+  if (pin < simhw::MAX_PINS && mode == INPUT) g_pins[pin].attached = false;
+}
+void digitalWrite(uint8_t, uint8_t) {}
+uint32_t analogWriteResolution(uint32_t bits) {
+  uint32_t old = g_pwm_bits;
+  g_pwm_bits = bits;
+  return old;
+}
+void analogWriteFrequency(uint8_t pin, float hz) {
+  if (pin < simhw::MAX_PINS) g_pwm_hz[pin] = hz;
+}
+// A duty of 0 means no pulses (a relaxed servo); otherwise the pulse width
+// follows from duty, resolution and frequency, exactly as on the hardware.
+void analogWrite(uint8_t pin, int value) {
+  if (pin >= simhw::MAX_PINS) return;
+  if (value <= 0) {
+    g_pins[pin].attached = false;
+    return;
+  }
+  float hz = g_pwm_hz[pin] > 0 ? g_pwm_hz[pin] : 488.28f;
+  g_pins[pin].us = (int)lroundf((float)value / (1u << g_pwm_bits) * (1e6f / hz));
+  g_pins[pin].attached = true;
+  g_pins[pin].writes++;
+}
+
 // =====================================================================
 // I2C + MPU6050 (register-level, address 0x68)
 // =====================================================================