refactor: move the layer state coordinator into its own module

layerState.js held both the share-link layer codec and the coordinator
that restores layer choices into the running app and persists them to
browser storage. Move the coordinator, unchanged, to
layerStateCoordinator.js so the codec stays a pure data module that code
outside the browser can use to write share links. The registry stays in
layerState.js, where the token tooling reads it, and the aircraft
barrel re-exports both.

src/layers/aircraft/index.js

@@ -9,6 +9,7 @@ export * from '../../data/cockpitContactDot.js';
 export * from '../../data/contactMatch.js';
 export * from '../../data/iconOrientation.js';
 export * from '../../data/layerState.js';
+export * from '../../data/layerStateCoordinator.js';
 export * from '../../data/modelVisualAnchor.js';
 export * from '../../data/motionModel.js';
 export * from '../../data/renderAltitude.js';