refactor(street-level): rename the Mapillary layer to street-level

Pure move: the layer id, panel id, CSS prefix, classes, exports and config
paths become provider-neutral (street-level, #street-level-panel, sl-);
the Mapillary-specific modules move under providers/mapillary/. Behaviour
is unchanged. The two sprite collections now register under distinct ids
instead of overwriting each other under 'mapillary'.

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

src/data/layerState.js

@@ -498,7 +498,6 @@ export const LAYER_STATE_REGISTRY = Object.freeze([
     disposition: 'enabled-only',
   }),
   Object.freeze({ id: 'local-firms', token: 'w', disposition: 'enabled-only' }),
-  Object.freeze({ id: 'mapillary', token: '3', disposition: 'enabled-only' }),
   Object.freeze({
     id: 'military',
     token: 'm',
@@ -538,6 +537,11 @@ export const LAYER_STATE_REGISTRY = Object.freeze([
     disposition: 'enabled+options',
     optionOwner: 'satellites',
   }),
+  Object.freeze({
+    id: 'street-level',
+    token: '3',
+    disposition: 'enabled-only',
+  }),
   Object.freeze({
     id: 'telegeography-submarine-cables',
     token: 'u',