Draft: shared protocol, remote firmware, project docs

Not yet verified on hardware.

- shared/HexapodProtocol: CmdPacket (now 20 bytes, adds remote_roll /
  remote_pitch), FLAG_* bits and radio settings as the single protocol
  definition; static payload size = sizeof(CmdPacket) on both radios.
- robot: use the shared protocol; vx = forward (harness w/x <-> q/e);
  InputMapper adds remote tilt on top of the right stick when
  FLAG_REMOTE_GYRO is set, and robot.ino no longer zeroes stick
  roll/pitch when it's off.
- remote (Teensy 4.1): Sticks (calibration, EEPROM), RemoteIMU,
  RemoteState (interlocks, link-loss disarm, smoothing), PacketBuilder,
  RadioLink, NextionUI, SerialConsole.
- CLAUDE.md, README.md, remote/README.md, remote/NEXTION.md.

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

2026-current/remote/UiTypes.h

@@ -0,0 +1,45 @@
+#pragma once
+#include <Arduino.h>
+
+// Operator commands. Produced by the Nextion touchscreen (NextionUI) and by
+// the USB serial console (SerialConsole) through the same path, so the
+// remote can be fully exercised on the bench without the display attached.
+enum class UiCmd : uint8_t {
+  None = 0,
+  ToggleArm,
+  Disarm,              // unconditional - the big red button
+  ToggleStand,
+  ToggleGait,          // tripod <-> wave
+  ToggleWalkMode,      // direct (A) <-> heading-hold (B)
+  ToggleRStickXlate,   // right stick: rotation <-> translation
+  ToggleRemoteGyro,
+  ToggleRobotGyro,
+  SetSpeed,            // value = 0..255
+  SpeedUp,             // serial console only
+  SpeedDown,           // serial console only
+  ZeroGyro,            // capture the handset's current attitude as "level"
+  CalStartSave,        // start sweep calibration, or save it if running
+  CalCancel,
+};
+
+struct UiEvent {
+  UiCmd cmd = UiCmd::None;
+  uint8_t value = 0;
+};
+
+// Everything the display shows. The remote is authoritative: the Nextion
+// only sends requests, and always renders what's in here.
+struct UiView {
+  bool armed = false;
+  bool stand = false;
+  bool gait_wave = false;
+  bool mode_b = false;
+  bool rstick_xlate = false;
+  bool remote_gyro = false;
+  bool robot_gyro = false;
+  bool calibrating = false;
+  uint8_t speed_target = 0;
+  bool link_ok = false;
+  uint8_t link_pct = 0;
+  const char* message = "";   // always a string literal - NextionUI diffs it by pointer
+};