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/README.md

@@ -7,7 +7,7 @@ simulation is exactly the code you flash to the Teensy. `robot/` has no
 `#ifdef SIM` anywhere.
 
 ```
-robot/ (unchanged) ──► PlatformIO + Teensy core ──► Teensy 4.0 firmware
+robot/ (unchanged) ──► PlatformIO + Teensy core ──► Teensy 3.6 firmware
                    └─► CMake + g++ + sim/shim/  ──► sim/build/hexapod_sim.dll ──► Unity
 ```
 
@@ -17,7 +17,7 @@ robot/ (unchanged) ──► PlatformIO + Teensy core ──► Teensy 4.0 firmw
 
 | Firmware uses | Simulated as |
 |---|---|
-| `Servo::writeMicroseconds()` | the pulse stored per pin, decoded back to angles with `Config.h`'s `SERVO_US_*` |
+| `analogWrite()` hardware PWM (how `ServoDriver` drives the servos) | the pulse width per pin, worked out from duty, resolution and frequency, then decoded back to angles through `Config.h`'s per-servo `SERVOS` table |
 | `Wire` + MPU6050 registers | a register-level fake MPU6050 at 0x68, fed from the simulated body's tilt and rotation |
 | `RF24` | a simulated radio: packets are received only if channel, address, data rate and **payload size** match, and the RX FIFO holds 3 |
 | `millis()` / `micros()` / `Serial` | a simulated clock that Unity advances, and captured serial I/O |
@@ -114,7 +114,9 @@ component to the scene yourself.
 ## What is not simulated
 
 - Physics (mass, falling, slipping, servo torque and speed).
-- Servo calibration. The sim decodes pulses with `Config.h`'s single
-  `SERVO_US_AT_0DEG` / `SERVO_US_PER_DEG`, i.e. what the firmware *intends*,
-  not per-servo offsets or directions.
+- Whether the calibration matches the real servos. The sim decodes pulses
+  through the same `SERVOS` table the firmware uses, so it shows what the
+  firmware *intends*, including pulse-limit clamping (which is how it
+  caught the old ±90° coxa offsets). Whether a real servo turns that way is
+  a bench check.
 - The remote firmware. `SimRemote.cs` mirrors its packet rules instead.