Sign test: measure ALL gimbal axes + self-healing altitude supervisor; link diagnostics

- Sign test measures rate response on every gimbal axis and picks the one
  that actually answers the differential push -> pitchIndex is now MEASURED
  per ship (build orientation no longer matters). Verified both-direction
  response accepted at half threshold. Tilt guard watches all axes.
- Altitude supervisor: drifting out of the measuring band re-centers and
  retries instead of aborting; single 7-min deadline. Faster hover trim
  (0.05 -> 0.12, matches verified Ki_climb) plus an 8 s settle phase.
- Single-balloon ships: sign test marks itself done, FLY zeroes u_diff.
- Cockpit terminal now explains link status (OFFLINE checklist); autopilot
  standby screen warns loudly when no modem is attached.
- Failure text points at cross-wired links (both burners firing on one pulse).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -39,9 +39,10 @@ console. Pitch and altitude keep self-learning in flight. The wizard can be
 re-run any time: `ap setup`, press `S` in standby, or menu choice 1.
 
 Balloon orientation does **not** need to match any particular side of the
-computer: sensors are found by type, wiring is mapped by the wizard, and the
-pitch sign is measured — the only physical requirement is both balloons on the
-fore/aft line (the axis the gimbal reports as pitch).
+computer — or any particular build direction: sensors are found by type,
+wiring is mapped by the wizard, and the sign test measures **which gimbal
+axis** responds to the push (saved as `pitchIndex`) along with its sign. The
+only physical requirement is two balloons spaced along the hull.
 
 ## Roles