feat(street-level): Google Street View as the second imagery provider

Google Street View registers beside Mapillary as provider `google`. It runs
on the Maps JavaScript API with the browser GOOGLE_MAPS_API_KEY, loaded on
first use (mapsLoader.js), and uses Google's own StreetViewPanorama as its
viewer adapter, emitting provider-neutral poses (address and month in the
caption, a link to Google Maps, steps along Google's arrows, FOLLOW on
Google 3D). Its chip starts off because every panorama is billed to the
key; the share option is `g`.

Google offers no coverage layer for other maps, so the provider draws
none: with it on, a click on bare ground at street zoom opens its nearest
Google-collected outdoor panorama (groundClick.js). A key Google refuses
reads KEY REJECTED and fails a pending open at once; a lookup Google never
answers fails after 10 s.

Core: providers may declare `groundClick` and `defaultOn`; poses may carry
`capturedAtPrecision` and `title`; the coverage line keeps every
provider's hint; opening one provider's image releases another's
prewarmed viewer; FIT/FILL hides for viewers without render modes. CSP
script-src admits https://maps.googleapis.com. The browser gate gains two
Street View steps (the keyed one skips as 'no Google key' in CI).

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

src/ui/streetLevelPresentation.test.mjs

@@ -388,3 +388,49 @@ test('FOLLOW is disabled off Google 3D and says where to switch', () => {
   );
   assert.equal(closed.viewer.follow.disabled, true, 'nothing to follow');
 });
+
+test('a Street View caption names the place, dates it by month, and offers no FIT/FILL', () => {
+  const view = presentStreetLevelPanel(
+    snapshot({
+      enabled: true,
+      street: {
+        open: true,
+        providerId: 'google',
+        providerName: 'Google Street View',
+        providerLabel: 'STREET VIEW',
+        imageId: 'pano-1',
+        title: '1014 10th St',
+        creator: 'Google',
+        capturedAt: Date.UTC(2023, 0, 1),
+        capturedAtPrecision: 'month',
+        bearing: 0,
+        isPano: true,
+        renderModes: false,
+        externalUrl:
+          'https://www.google.com/maps/@?api=1&map_action=pano&pano=pano-1',
+      },
+    }),
+  );
+  assert.equal(view.viewer.captionLeft, '1014 10th St · Image by Google');
+  assert.equal(view.viewer.captionRight, '360° · 0° · 2023-01');
+  assert.equal(view.viewer.linkLabel, 'STREET VIEW ↗');
+  assert.equal(view.viewer.renderModes, false);
+});
+
+test('the meta line keeps the sequence count and adds the other providers’ hints', () => {
+  const view = presentStreetLevelPanel(
+    snapshot({
+      enabled: true,
+      coverage: {
+        loading: false,
+        count: 2514,
+        hint: 'click a street to open Street View',
+        error: null,
+      },
+    }),
+  );
+  assert.equal(
+    view.meta,
+    `${(2514).toLocaleString()} sequences in view · click a line for its photos · click a street to open Street View`,
+  );
+});