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/SmoothedValue.h

@@ -0,0 +1,26 @@
+#pragma once
+
+// Rate-limited setpoint smoother - identical to robot/SmoothedValue.h (kept
+// as a copy rather than moved to shared/ so the robot sketch stays untouched).
+// Used for UI-driven setpoints that would otherwise step: speed scale and
+// the remote-tilt fade.
+struct SmoothedValue {
+  float current = 0;
+  float target  = 0;
+  float max_rate;   // units per second
+
+  explicit SmoothedValue(float rate = 100.0f) : max_rate(rate) {}
+
+  void setTarget(float t) { target = t; }
+
+  float update(float dt) {
+    float delta = target - current;
+    float max_step = max_rate * dt;
+    if (delta > max_step) delta = max_step;
+    else if (delta < -max_step) delta = -max_step;
+    current += delta;
+    return current;
+  }
+
+  void reset(float v) { current = target = v; }
+};