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/README.md

@@ -0,0 +1,32 @@
+# Hexapod
+
+A six-legged walking robot (Teensy 4.0) and its handheld remote
+(Teensy 4.1 + Nextion touchscreen), linked over nRF24L01.
+
+```
+robot/    robot firmware: IK, gait, body pose, IMU stabilization, state machine
+remote/   remote firmware: 2 x 3-axis sticks, MPU6050 tilt, Nextion UI, RF24 TX
+shared/   HexapodProtocol: the CmdPacket wire format + radio settings used by both
+scripts/  PlatformIO helper (per-environment sketch folder)
+```
+
+## Build (PlatformIO)
+
+```
+pio run                    # build both
+pio run -e robot -t upload
+pio run -e remote -t upload
+pio device monitor -e robot
+```
+
+## Where to go next
+
+- **[robot/README.md](robot/README.md)**: placeholder geometry to measure,
+  the bench-check checklist, and the serial test harness for driving the
+  robot without a remote.
+- **[remote/README.md](remote/README.md)**: wiring, control scheme, stick
+  calibration, and the remote's serial console.
+- **[remote/NEXTION.md](remote/NEXTION.md)**: how to build the touchscreen
+  HMI.
+- **[shared/HexapodProtocol/HexapodProtocol.h](shared/HexapodProtocol/HexapodProtocol.h)**:
+  the protocol. Change it only by reflashing both boards.