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/fr.json

@@ -1660,6 +1660,9 @@
   "REGIONAL NEWS": "ACTUS RÉGIONALES",
   "{label} · {radius} AIR/SEA WINDOW": "{label} · AIR/MER {radius}",
   "{scope} · INSTALLATIONS {coverage}": "{scope} · INSTALLATIONS : {coverage}",
+  "MILITARY FEED OFF · PARTIAL PICTURE": "FLUX MILITAIRE COUPÉ · SITUATION PARTIELLE",
+  "FLIGHTS FEED OFF · PARTIAL PICTURE": "FLUX DES VOLS COUPÉ · SITUATION PARTIELLE",
+  "NEARBY AIRCRAFT INCOMPLETE · NOT AN ALL-CLEAR": "AÉRONEFS PROCHES INCOMPLETS · PAS UN FEU VERT",
   "CONTEXT STANDBY": "CONTEXTE EN VEILLE",
   "ENABLE GLOBAL CONTEXT FOR PROXIMITY PINGS": "ACTIVER LE CONTEXTE GLOBAL POUR LES PINGS DE PROXIMITÉ",
   "CONTACT LOST · LAST KNOWN READOUT · NOT AN ALL-CLEAR": "CONTACT PERDU · DERNIER RELEVÉ CONNU · PAS UN FEU VERT",