refactor: export infrastructure layers with explicit application callbacks

docs/INFRASTRUCTURE-LAYERS.md

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+# Reusing infrastructure layers
+
+`gods-eye-view/infrastructure` exports `createInfrastructureLayers(services)`.
+It returns fresh datacenter and dam layers in that order, with the existing IDs,
+appearance, label budgets and bundled public datasets. Importing the module or
+calling the factory does not load data, create a viewer, or start the application.
+The asset URLs resolve relative to the module; Vite rewrites them for production
+base paths. This browser source export expects a Vite-compatible asset build.
+
+Pass the application's existing functions:
+
+```js
+import { createInfrastructureLayers } from 'gods-eye-view/infrastructure';
+
+const layers = createInfrastructureLayers({
+  overlayHost: { setEntries, setVisible, clearSource },
+  registerEntityContext,
+  selectEntityContext,
+  clearSelectedEntityContextForLayer,
+  removeEntityContextsForLayer,
+  governorRequestRender,
+});
+
+// Register these layers with the existing data-layer manager and viewer.
+```
+
+| Function | Arguments / responsibility |
+| --- | --- |
+| `overlayHost.setEntries` | `(sourceId, entries, options)`; publish the existing infrastructure overlay records and paint budget |
+| `overlayHost.setVisible` | `(sourceId, visible)`; toggle a source |
+| `overlayHost.clearSource` | `(sourceId)`; remove that source's overlay entries |
+| `registerEntityContext` | `(entity, metadata)`; register selectable feature metadata, including the owning layer and data source |
+| `selectEntityContext` | `(entity)`; select that registered feature |
+| `clearSelectedEntityContextForLayer` | `(layerId)`; clear selection only if owned by this layer |
+| `removeEntityContextsForLayer` | `(layerId)`; remove records owned by the layer on destruction or failed setup |
+| `governorRequestRender` | `(reason)`; request a frame through the existing render scheduler |
+
+Each returned layer supports `init(viewer)`, `enable(viewer)`, `disable(viewer)`,
+`update(viewer)`, `destroy(viewer)`, `getStats()` and `getLodDiagnostics()`.
+Use the same viewer for the instance's entire lifetime. Each viewer/context/overlay
+host permits one live instance per layer ID; destroy an old instance before
+replacing it. Separate applications may use identical IDs with separate hosts.
+Callbacks must be ready before enable and remain usable through destruction.
+
+Disable retains the loaded dataset for reuse and clears selection and listeners.
+Concurrent enables share one load. Destroy is permanent, aborts pending fetches,
+discards late results, and clears the owned data source, context records, overlays,
+input handler and listeners. The layer never creates an application context store,
+overlay host, viewer, or render scheduler. The consumer must resolve one compatible
+Cesium installation shared with its viewer; it must not bundle separate copies.
+
+`gods-eye-view/infrastructure/geojson` exports the lower-level
+`createLocalGeoJsonLayer(options, services)` and existing infrastructure overlay
+helpers. `gods-eye-view/infrastructure/lod` exports the existing LOD policy helpers.
+The standalone app's `src/data/localGeojson.js` keeps its original single-argument
+factory and supplies its existing functions. Other consumers should use the package
+exports, which do not import standalone application globals.
+
+Dataset files and source/license notices remain under `src/data/local_data/`.
+Their input counts are 4,351 datacenter features and 704 dam features. Cesium may
+expand multipart geometries into multiple entities; entity and stem counts are
+different measurements. This change does not refresh or relicense the datasets.