Auto-resume flight across chunk unload/reload

When the ship's chunk unloads the CC computer powers off and its redstone
outputs reset to 0, so on return the ship dropped and the pilot had to
re-ENGAGE every time. Flight state now survives the reboot:

- engaged.txt flag written while flying, cleared on pilot STOP.
- On boot, if engaged + profile present: drive the hover baseline
  immediately (closes the fall gap), then runStandby(true) re-enters the
  flight loop automatically with the persisted target -- no manual ENGAGE.
- runFly drives hover before its first sleep so no entry path leaves a
  0-output gap.
- Cleanup no longer lifts a PARKED ship: Ctrl+T out of standby holds hover
  only when engaged, else valves off.
- engaged.txt registered as per-ship state (gitignore, installer keep/reset,
  menu reset, build excludes).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -9,6 +9,7 @@ files/*/calib.txt
 files/*/sides.txt
 files/*/target.txt
 files/*/settings.txt
+files/*/engaged.txt
 files/*/scan.txt
 files/*/pid_gains.txt
 files/*/.installed_*