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/layers/streetLevel/providers/google/viewer.test.mjs

@@ -130,11 +130,8 @@ test('an open overtaken by a newer one only shows the newer panorama', async ()
   assert.ok(!poses.some((pose) => pose.imageId === 'pano-a'));
 });
 
-test('unmounting removes the element and every listener; prewarm builds no panorama', async () => {
-  const { fake, loader, viewer, host } = setup();
-  await viewer.prewarm(host);
-  assert.deepEqual(loader.imports, ['streetView']);
-  assert.equal(fake.built.length, 0, 'a panorama is billed: none on prewarm');
+test('unmounting removes the element and every listener', async () => {
+  const { fake, viewer, host } = setup();
   await viewer.mount(host);
   const [panorama] = fake.built;
   assert.ok(panorama.listenerCount() > 0);
@@ -144,6 +141,12 @@ test('unmounting removes the element and every listener; prewarm builds no panor
   await assert.rejects(viewer.open('pano-a'), /not mounted/);
 });
 
+test('there is no prewarm: Google\u2019s script loads on first use only, never on another map', () => {
+  const { viewer, loader } = setup();
+  assert.equal(viewer.prewarm, undefined);
+  assert.deepEqual(loader.imports, []);
+});
+
 test('a key Google refuses fails the open at once, not after the timeout', async () => {
   const { fake, loader, viewer, host } = setup();
   await viewer.mount(host);