Adds bench vs model power arrangements, the both-USB-plus-5V-jumper
hazard, current budget, diode drop margin, and a deliberate test for the
case the 400ms failsafe cannot cover.
Adds bring-up order (pair the pad before wiring, verify the port map with
DEBUG_MOTORS before trusting it), the tank drive control table, the extended
link protocol, and the wiring failure modes.
jessikitty