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/layers/streetLevel/state.js

@@ -0,0 +1,68 @@
+/** Mutable per-layer state, created once per layer instance. */
+export function createState({ services }) {
+  return {
+    services,
+    viewer: null,
+    enabled: false,
+    initialized: false,
+    destroyed: false,
+    status: null,
+    statusError: null,
+    keyRequired: false,
+    /** Cesium.Credit shown while enabled (CC BY-SA attribution). */
+    credit: null,
+    listeners: new Set(),
+    notifyScheduled: false,
+
+    coverage: {
+      zoom: null,
+      /** @type {Map<string, {primitive: object|null, sequences: Map<string, object>, count: number}>} */
+      tiles: new Map(),
+      /** Tiles from the previous zoom, kept on screen until replacements land. */
+      stale: new Map(),
+      staleTimer: null,
+      pending: new Map(),
+      generation: 0,
+      loading: 0,
+      lastError: null,
+      debounceTimer: null,
+      removeCameraListener: null,
+      terrainReady: null,
+      hint: '',
+      kind: null,
+      filter: { pano: 'all', sinceMs: null },
+    },
+
+    sequence: {
+      selectedId: null,
+      images: [],
+      /** @type {Map<string, Array<object>>} recent sequences' thinned images */
+      cache: new Map(),
+      collection: null,
+      loading: false,
+      abort: null,
+    },
+
+    street: {
+      bridge: null,
+      container: null,
+      open: false,
+      follow: false,
+      imageId: null,
+      position: null,
+      bearing: null,
+      tilt: null,
+      isPano: false,
+      capturedAt: null,
+      sequenceId: null,
+      loading: false,
+      error: null,
+      marker: null,
+      markerCollection: null,
+      /** 'letterbox' shows the whole image; 'fill' crops it to the frame. */
+      renderMode: 'letterbox',
+    },
+
+    clickHandler: null,
+  };
+}