feat(street-level): OPEN STREET VIEW, and Street View only on Google 3D

- OPEN STREET VIEW in the PROVIDERS row opens Street View's nearest
  panorama at the ground under the middle of the screen, without moving
  the camera: Street View no longer needs a pointer. It is disabled (and
  says so) until the camera is at street zoom.
- Off the Google 3D map Street View does not appear at all: no chip,
  legend swatch, globe credit, layer source or button, and Google's script
  is not loaded (the viewer has no prewarm; the script loads on first use).
  The share option keeps the user's choice for when Google 3D returns.
- A ground click measures the camera height at the click rather than
  reading the cached flag.
- A chip without a usable key explains it instead of lighting; it darkens
  beside a lit chip, and the other chips keep switching, so a refused
  Street View key cannot lock Mapillary out.
- The gate checks that nothing of Street View shows off Google 3D even when
  a share link switches it on, presses OPEN STREET VIEW on Google 3D, and
  asserts that each chip it switches really switched.

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

src/app/layers/streetLevel.test.mjs

@@ -16,12 +16,9 @@ test('each provider starts as its share-link option does, so a fresh page and a
     },
   });
   const options = createDefaultLayerState().options['street-level'];
-  const providers = layer.getUIState().providers;
-  assert.deepEqual(
-    providers.map((p) => p.id),
-    layer.providerIds,
-  );
-  for (const provider of providers)
-    assert.equal(provider.on, options[provider.id], provider.id);
+  // Every registered provider, listed on this map or not.
+  const started = layer.getParams();
+  for (const id of layer.providerIds)
+    assert.equal(started[id], options[id], id);
   assert.equal(options.google, false, 'Street View is billed: off');
 });