Migrates the 4WD control input from SDL2/Xbox gamepad to a serial RC
receiver per doc/joystick.md's functional spec: CH1 steering, CH2
throttle, CH5 emergency brake (highest priority), CH7 speed mode
(0.3/0.6 m/s), with a 200ms fail-safe that forces an immediate stop
on signal loss. Channel mapping, deadzones, port, and baudrate are
all configurable via --rc_* CLI flags. LiDAR avoidance, jerk-limited
motion profile, and wheel-fault detection are unchanged.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
robin