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/Comms.cpp

@@ -3,15 +3,19 @@
 #include <RF24.h>
 #include <SPI.h>
 
+static_assert(HXP_RADIO_DATA_RATE == RF24_250KBPS && HXP_RADIO_PA_LEVEL == RF24_PA_LOW,
+              "HexapodProtocol.h radio enum values out of sync with RF24.h");
+
 static RF24 radio(RADIO_CE_PIN, RADIO_CSN_PIN);
 
 bool Comms::begin() {
   radio_present_ = radio.begin();
   if (radio_present_) {
-    radio.openReadingPipe(1, RADIO_ADDRESS);
-    radio.setPALevel(RF24_PA_LOW);
-    radio.setDataRate(RF24_250KBPS);
-    radio.setChannel(96);          // pick one clear of your local Wi-Fi
+    radio.setPayloadSize(HXP_RADIO_PAYLOAD);   // mismatched protocol versions won't be received at all
+    radio.openReadingPipe(1, HXP_RADIO_ADDRESS);
+    radio.setPALevel((rf24_pa_dbm_e)HXP_RADIO_PA_LEVEL);
+    radio.setDataRate((rf24_datarate_e)HXP_RADIO_DATA_RATE);
+    radio.setChannel(HXP_RADIO_CHANNEL);
     radio.startListening();
   }
   return radio_present_;