Read flight and military billboard state from Core's mirror

Flights and military now add their billboards through addBillboard and
write show, position, scale, rotation, size and distance scaling through
setBillboard, which keeps Core's copy in src/data/billboardMirror.js.
Their reads go to billboardState instead of the Cesium billboard, so the
layers no longer read back what they pushed to the renderer.

A mirrored billboard needs an explicit width and height, because unset
Cesium reports the loaded image's size. Colour is not mirrored yet: the
cyber-sonar theme writes it too and tells the writers apart by the live
value, so it moves with the effects port.

scripts/package-boundaries.json

@@ -1315,6 +1315,7 @@
       "src/layers/flights/policy.js",
       "src/layers/flights/queries.js",
       "src/layers/flights/rendering.js",
+      "src/data/billboardMirror.js",
       "src/layers/aircraft/visualState.js",
       "src/layers/flights/state.js",
       "src/layers/flights/testing.js",
@@ -1375,6 +1376,7 @@
       "src/layers/military/policy.js",
       "src/layers/military/queries.js",
       "src/layers/military/rendering.js",
+      "src/data/billboardMirror.js",
       "src/layers/aircraft/visualState.js",
       "src/layers/military/state.js",
       "src/layers/military/testing.js",
@@ -2320,6 +2322,7 @@
       "src/data/aircraftMeta.js",
       "src/data/aircraftNearbyPolicy.js",
       "src/data/aircraftRecession.js",
+      "src/data/billboardMirror.js",
       "src/data/aisLiveVessels.js",
       "src/data/alprCameras.js",
       "src/data/analystEngine.js",
@@ -3284,6 +3287,7 @@
       "src/data/aircraftMeta.js",
       "src/data/aircraftNearbyPolicy.js",
       "src/data/aircraftRecession.js",
+      "src/data/billboardMirror.js",
       "src/data/cctvCards.js",
       "src/data/cctvFootprint.js",
       "src/data/cctvGizmo.js",