Merge origin/main: keep the provider registry, slim it

main grew the Street Level provider registry while this branch removed it
(#982–#985: injected providers, an empty composition, the `r` switch field).
The registry, params, uiState and pick router come back as main has them and
the slimmed layer sits behind the provider contract:

- The core (index.js) drives providers as on main, without surface modes,
  ground casting, FOLLOW, prewarm and nearest-image lookups. A provider's key
  status is asked with a 10 s timeout and asked again on a switch-on while no
  key is known.
- Mapillary is mapillaryProvider.js over the slim coverage, sequences and
  viewer modules, which read the filter and the active flag from the provider
  context.
- The viewer host mounts one provider adapter at a time, no prewarm.
- The panel has a chip per provider again (the pill switches the layer);
  no legend, EXPAND stays the Fullscreen API.
- The contract drops what no provider implements: groundCaster, meshSampler,
  getSurface/setSurface, nearestImage, prewarm, reportError, the legend and
  surface fields of the UI snapshot.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/standalone/layerSources.js

@@ -1,3 +1,5 @@
+import { createDirectionsSource } from '../layers/directions/source.js';
+import { createRecentImagerySource } from '../layers/recentImagery/source.js';
 import { createOpenFreeMapSource } from '../sources/openFreeMap.js';
 import {
   createFlightSource,
@@ -22,10 +24,14 @@ import { createReferenceSources } from '../sources/reference.js';
 export { createReferenceSources as createStandaloneReferenceSources } from '../sources/reference.js';
 
 /** Select standalone providers without starting their acquisition. */
-export function createStandaloneLayerSources() {
+export function createStandaloneLayerSources(overrides = {}) {
+  if (!overrides || typeof overrides !== 'object' || Array.isArray(overrides))
+    throw new TypeError('Source overrides must be an object');
   const mapTiles = createOpenFreeMapSource();
-  return {
+  const defaults = {
     ...createReferenceSources(),
+    directions: createDirectionsSource(),
+    'recent-imagery': createRecentImagerySource(),
     flights: createFlightSource(),
     military: createMilitarySource(),
     vessels: createVesselSource({
@@ -51,4 +57,9 @@ export function createStandaloneLayerSources() {
       token: import.meta.env?.MAPILLARY_CLIENT_TOKEN || '',
     }),
   };
+  for (const name of Object.keys(overrides)) {
+    if (!Object.hasOwn(defaults, name))
+      throw new TypeError(`Unknown source: ${name}`);
+  }
+  return { ...defaults, ...overrides };
 }