feat(street-level): one imagery source at a time; IC8 review fixes

- One provider is lit at a time: lighting a chip darkens the others, and a
  chip click records every registered provider's switch in one update so
  the share link keeps the swap (also off Google 3D, where Street View is
  not listed). The layer starts with the first default-on provider
  (Mapillary, free); params that light several keep the one already on,
  so reapplying them never flips (litByParams). The now-unreachable
  "several lit" chip paths are gone.
- Leaving Google 3D during a Street View lookup ends it without an error
  or a stuck loading state (openImage's early return resets it; the
  lookup loop rechecks availability).
- A source swap during a lookup no longer reports "no imagery".
- Street View lit off Google 3D says the panel needs the Google 3D map.
- Comments trimmed to the why; keySetupCore.test.mjs back to upstream's
  formatting plus the one new test (was a 551-line reformat).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/streetLevel/registry.js

@@ -1,9 +1,7 @@
 import { encodeIdSwitches } from '../../data/idSwitches.js';
 
-/** The imagery filters a provider can honour. */
 export const IMAGERY_FILTERS = Object.freeze(['pano', 'since']);
 
-/** The filters `provider` honours: both, unless it says otherwise. */
 export function filtersOf(provider) {
   return provider?.filters ?? IMAGERY_FILTERS;
 }
@@ -19,11 +17,11 @@ export function filtersOf(provider) {
  * @property {string} pickPrefix    Every primitive id the provider creates starts with it.
  * @property {{coverage: string}} colors   The source's one colour, from policy.js PROVIDER_COLORS.
  * @property {{html: string}} credit   On-globe attribution while the provider is active.
- * @property {boolean} [groundClick]   No coverage to click: a click on the ground at street zoom opens its nearest image.
- * @property {string} [requiresMapStack]   Usable only on this map stack (Google Street View: 'photoreal', per Google's terms).
- * @property {boolean} [defaultOn]     Switched on until the user says otherwise (default true); a share link without its switch keeps it.
- * @property {{kind: 'view-cone', color: string}} [marker]   On-globe marker for its open image (default GEV's pin): Street View's blue field-of-view cone.
- * @property {Array<'pano'|'since'>} [filters]   The imagery filters it honours (default both); the panel hides a filter no lit provider honours.
+ * @property {boolean} [groundClick]   No coverage: a ground click at street zoom opens its nearest image.
+ * @property {string} [requiresMapStack]   Usable only on this map stack.
+ * @property {boolean} [defaultOn]     Default true.
+ * @property {{kind: 'view-cone', color: string}} [marker]   Default: GEV's pin.
+ * @property {Array<'pano'|'since'>} [filters]   Filters it honours (default both).
  * @property {(context: ProviderContext) => ProviderInstance} create
  *
  * @typedef {object} ProviderContext   Handed to `create()` once by the core.