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/uiState.js

@@ -45,6 +45,7 @@ export function summarizeCoverage(providers) {
  */
 export function composeUIState({
   enabled,
+  groundClickReady = false,
   filter,
   providers,
   street,
@@ -63,6 +64,8 @@ export function composeUIState({
     legend.push({ key: 'selected', label: 'Selected', color: COLORS.selected });
   return {
     enabled,
+    /** The camera is at street zoom: a ground-click provider can open here. */
+    groundClickReady: groundClickReady === true,
     keyRequired,
     keyRejected,
     filter: { ...filter },