Stop Navara's memory growth on engine switches, hide polygon zones reliably, and drop the Cesium camera rig

- Navara 0.2.1 never frees pick batch ids, and the mover banks rebuilt
  their instanced meshes on each attach, leaking about 260 KiB of
  WebAssembly memory per switch. A per-view pool hands released ids back
  out; the long soak now asserts native growth of at most 32 KiB per switch.
- Navara 0.2.1 sometimes drops the first show:false update on a new
  vector layer, so a zone turned off right after a switch back stayed
  drawn. Polygon displays hide by deleting their layers and rebuild them
  when shown.
- Camera verbs drive both engines through the globe contract; the Cesium
  viewer rig and the tests of states it can no longer reach are gone.
- Flights and military tracking share src/layers/aircraft/tracking.js.
- The geo import scenario reads movers only where the engine has them.
- Add the Navara section to docs/CURRENT-STATE.md and a changelog fragment.

scripts/qa-navara-geo-import.mjs

@@ -176,8 +176,8 @@ await strict.run(
         rows: document.querySelectorAll('#geo-import-list .geo-import-row')
           .length,
         hint: document.getElementById('geo-import-hint')?.textContent || '',
-        pins: window.__godsEyeView.engine.movers
-          .list()
+        // Movers are a Navara capability; Cesium draws the pins as entities.
+        pins: (window.__godsEyeView.engine.movers?.list() ?? [])
           .filter(({ id }) => id.startsWith('geo-import-'))
           .reduce((n, set) => n + set.count, 0),
       }));