Merge branch 'main' into feat/aqhi

Port to current main: main reserved layer-state token 0 for street-level, so
air-quality takes the next free token, 4 (registry, ledger, and the allocation
tests shift by one). Main moved source contracts into sourceComposition.js, so
air-quality registers its getSnapshot contract there. Package boundaries keep
main's lists plus this branch's air-quality modules and packages.

src/sources/reference.js

@@ -2,6 +2,7 @@ import { createUsgsEarthquakeSource } from '../layers/earthquakes/source.js';
 import { createEcccAirQualitySource } from '../layers/airQuality/source.js';
 import { createWfigsPerimeterSource } from '../layers/perimeters/source.js';
 import { createBundledCableSource } from '../layers/submarineCables/bundledSource.js';
+import { createAdsbGnssSource } from '../layers/gnss/source.js';
 
 /** Construct the existing reference feeds independently of application setup. */
 export function createReferenceSources() {
@@ -10,5 +11,6 @@ export function createReferenceSources() {
     'air-quality': createEcccAirQualitySource(),
     'fire-perimeters': createWfigsPerimeterSource(),
     cables: createBundledCableSource(),
+    'gnss-integrity': createAdsbGnssSource(),
   };
 }