fix(street-level): point a key-gated layer at Street View; button beside the hint

Review of #966: with a Google Maps key but no Mapillary token, switching
Street Level on read KEY REQUIRED / "Needs MAPILLARY_CLIENT_TOKEN" with
nothing about Street View, which stayed off (billing), so the layer looked
broken.

- While the switched-on providers lack their keys, the layer reports the
  switched-off ones that would draw with a key already set
  (keyAlternatives: Street View on Google 3D with a Google key). The
  panel's KEY REQUIRED tooltip, its coverage line and the layer row's
  tooltip then read "Needs MAPILLARY_CLIENT_TOKEN — add it in Provider
  Settings, or light STREET VIEW to use your Google Maps key"
  (keySetupWithAlternatives). Off Google 3D the plain KEY REQUIRED stays.
  Street View stays off by default.
- OPEN STREET VIEW moves beside the coverage hint: at the default panel
  width the PROVIDERS row has no room for it, so it wrapped onto a line of
  its own.
- The panel gate's corner drag names what lay under the pointer when it
  fails.

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

src/ui/styles/street-level.css

@@ -183,8 +183,20 @@ button.sl-status:focus-visible {
   border-color: rgba(255, 179, 0, 0.55);
 }
 
+/* The coverage hint and OPEN STREET VIEW share a line; the hint wraps. */
+.sl-meta-row {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+
+.sl-meta-row .sl-meta {
+  flex: 1 1 auto;
+  min-width: 0;
+}
+
 .sl-nearest-btn {
-  margin-left: auto;
+  flex: 0 0 auto;
 }
 
 .sl-nearest-btn[hidden] {