feat(street-level): Street View polish — name, filters, legend, marker

- The chip reads GOOGLE STREET VIEW (and its caption link likewise).
- Providers declare the imagery filters they honour (`filters`, default
  pano + since). Street View declares none: every panorama is 360° and it
  draws no coverage to thin, so its lookups ignore the filters and the
  panel hides IMAGERY and SINCE while it is the only lit provider.
- The legend lists only providers that draw coverage lines, with
  Selected only beside one: Street View alone shows no legend.
- Providers may pick their on-globe marker (`marker`); Street View's is a
  Google-blue field-of-view cone from a white-ringed dot, in place of
  GEV's amber pin, and switches back for a Mapillary photo.

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

src/layers/streetLevel/registry.test.mjs

@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
-import { requiresKeyIdFor, validateProviders } from './registry.js';
+import { filtersOf, requiresKeyIdFor, validateProviders } from './registry.js';
 
 const def = (overrides = {}) => ({
   id: 'mapillary',
@@ -101,3 +101,20 @@ test('requiresKeyIdFor is the shared key, or null once providers differ', () =>
   );
   assert.equal(requiresKeyIdFor([def({ requiresKeyId: null })]), null);
 });
+
+test('a provider may narrow the filters it honours and pick a view-cone marker', () => {
+  assert.deepEqual(filtersOf(def()), ['pano', 'since'], 'both by default');
+  const narrowed = def({
+    filters: [],
+    marker: { kind: 'view-cone', color: '#4285f4' },
+  });
+  assert.deepEqual(filtersOf(validateProviders([narrowed])[0]), []);
+  assert.throws(
+    () => validateProviders([def({ filters: ['colour'] })]),
+    /filters must list pano or since/,
+  );
+  assert.throws(
+    () => validateProviders([def({ marker: { kind: 'pegman' } })]),
+    /marker must be/,
+  );
+});