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/NextionUI.h

@@ -0,0 +1,42 @@
+#pragma once
+#include "UiTypes.h"
+#include "Config.h"
+
+// Nextion serial HMI driver. No Nextion library - the protocol is small:
+//
+//  Nextion -> remote: custom frames the HMI's touch events send with printh:
+//      '#' <len> <cmd> [value]        e.g. printh 23 01 41   (ToggleArm)
+//                                          printh 23 02 56 + prints hSpeed.val,1
+//    Command bytes are listed in NEXTION.md and in NextionUI.cpp.
+//    Native Nextion return frames (terminated FF FF FF) are also parsed so a
+//    display reset (0x88 "ready") triggers a full redraw.
+//
+//  remote -> Nextion: plain instructions ("bArm.txt=\"ARMED\"" + FF FF FF).
+//
+// The remote is authoritative: buttons are plain buttons (not dual-state),
+// they only send requests, and render() repaints whatever the remote state
+// actually is. A Nextion reboot or a dropped byte self-heals on the next
+// periodic full refresh.
+class NextionUI {
+public:
+  void begin();
+  bool poll(UiEvent& out);                 // call every loop; returns one decoded event at a time
+  void render(const UiView& v, uint32_t now_ms);
+
+private:
+  enum class Rx : uint8_t { Idle, CustomLen, CustomBody, Native };
+  Rx rx_ = Rx::Idle;
+  uint8_t body_[4];
+  uint8_t body_len_ = 0, body_got_ = 0;
+  uint8_t native_first_ = 0, native_len_ = 0, ff_run_ = 0;
+
+  UiView shown_;
+  bool force_full_ = true;
+  uint32_t last_full_ms_ = 0;
+  uint32_t last_link_ms_ = 0;
+
+  void cmd(const char* fmt, ...);
+  void pushState(const UiView& v, bool full);
+  void pushLink(const UiView& v);
+  bool decodeCustom(UiEvent& out);
+};