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.

server/providers/openai/toolDescriptions.js

@@ -135,7 +135,7 @@ export const ACTION_DESCRIPTIONS = {
   },
   control_cockpit: {
     description:
-      'Explicit Cockpit requests only: enter from a selected/tracked aircraft (establishes Contacts itself; no set_context_mode), exit, status, or next/previous. Explicit exit-and-show voice: voicePanel preview/settings (Voice Settings), no confirmation.',
+      'Explicit Cockpit requests only: enter from a selected/tracked aircraft (needs only its own Flights/Military layer on, not Contacts; opens Contacts itself, no set_context_mode), exit, status, or next/previous. Explicit exit-and-show voice: voicePanel preview/settings (Voice Settings), no confirmation.',
     $position: 1,
     parameters: {
       properties: {