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/tooling/streetLevelQa.test.mjs

@@ -515,15 +515,20 @@ test('evidence never carries a Mapillary token', () => {
 test('--strict accepts only the documented skips', () => {
   assert.deepEqual(
     [...STRICT_ALLOWED_SKIPS],
-    ['no Google 3D', 'fixtures only'],
+    ['no Google 3D', 'no Google key', 'fixtures only'],
   );
   assert.deepEqual(
     strictViolations([
       { reason: 'no Google 3D', label: 'terrain' },
+      { reason: 'no Google key', label: 'street view' },
       { reason: 'fixtures only', label: 'keyless page' },
       { reason: 'no Mapillary key', label: 'the keyed steps' },
+      { reason: 'Google key refused', label: 'street view' },
     ]),
-    [{ reason: 'no Mapillary key', label: 'the keyed steps' }],
+    [
+      { reason: 'no Mapillary key', label: 'the keyed steps' },
+      { reason: 'Google key refused', label: 'street view' },
+    ],
   );
 });