feat(cockpit): enter Cockpit with only the ridden aircraft's layer on

Cockpit entry no longer needs Contacts or both flight feeds: a civilian
aircraft needs Live Flights, a military one Military Flights. Contacts and
every other layer can be turned on or off before or during a session, and
turning off the ridden layer ends it. A Context mode change in flight still
blocks entry.

When the other air feed is off, Live Signals and the Contact card say
FLIGHTS FEED OFF or MILITARY FEED OFF · PARTIAL PICTURE instead of
presenting a partial picture as complete. Voice refuses entry with
subject-layer-off rather than contacts-inactive, and its tool description
says Contacts is not required.

Double-clicking the followed aircraft enters Cockpit through the same gate.
The Cockpit takes the scene's double-click before Cesium's stock handler,
which would otherwise untrack a followed aircraft whose model is a
primitive. The entry also shows under the Intel HUD readout, sharing the
Contacts button's face. A test keeps the classes the Cockpit adds to the
body from matching another element's rule.

src/i18n/locales/de.json

@@ -2087,6 +2087,9 @@
   "{value} KM/H": "{value} KM/H",
   "{label} · {radius} AIR/SEA WINDOW": "{label} · {radius} LUFT-/SEEFENSTER",
   "{scope} · INSTALLATIONS {coverage}": "{scope} · ANLAGEN {coverage}",
+  "MILITARY FEED OFF · PARTIAL PICTURE": "MILITÄR-FEED AUS · UNVOLLSTÄNDIGES LAGEBILD",
+  "FLIGHTS FEED OFF · PARTIAL PICTURE": "FLUG-FEED AUS · UNVOLLSTÄNDIGES LAGEBILD",
+  "NEARBY AIRCRAFT INCOMPLETE · NOT AN ALL-CLEAR": "FLUGZEUGE IN DER NÄHE UNVOLLSTÄNDIG · KEINE ENTWARNUNG",
   "SQUAWK {code} · {status}": "SQUAWK {code} · {status}",
   "ADS-B PRIORITY · {status}": "ADS-B-PRIORITÄT · {status}",
   "ADS-B EMERGENCY · {status}": "ADS-B-NOTFALL · {status}",