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/robot/InputMapper.cpp

@@ -56,5 +56,15 @@ MapperOutput InputMapper::map(const CmdPacket& p, float heading_deg, float dt) {
     out.pose.yaw_deg   = rz * MAX_TILT_DEG;
   }
 
+  // Remote handset tilt feedforward: its own packet fields, gated only by
+  // FLAG_REMOTE_GYRO, added on top of whatever the right stick commands (so
+  // it works in both right-stick sub-modes). Total tilt stays within MAX_TILT_DEG.
+  if (out.remote_gyro_enabled) {
+    out.pose.roll_deg  = constrain(out.pose.roll_deg  + normalize(p.remote_roll)  * MAX_TILT_DEG,
+                                   -MAX_TILT_DEG, MAX_TILT_DEG);
+    out.pose.pitch_deg = constrain(out.pose.pitch_deg + normalize(p.remote_pitch) * MAX_TILT_DEG,
+                                   -MAX_TILT_DEG, MAX_TILT_DEG);
+  }
+
   return out;
 }