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/app/catalog.test.mjs

@@ -93,7 +93,7 @@ test('controls bind catalog instances rather than similarly named defaults', ()
     'military-awareness',
     'military-installations',
     'rocket-launches',
-    'mapillary',
+    'street-level',
     'local-adsb',
   ];
   const layers = ids.map((id) => ({ id }));