Merge upstream/main into pr/google-street-view

Conflicts with upstream's Street Level provider composition and share-state
codec, resolved:

- Street View's switch moves from its own share option (`g`) to upstream's
  provider-switch field (`r`, e.g. `0.r.google-1`); a link without it keeps
  Street View off. Docs and the browser gate follow.
- createApplicationStreetLevel keeps upstream's injectable provider list;
  its default, once the application supplies its Street Level source, is
  Mapillary plus Google Street View. Without that source there are none, as
  upstream intends.
- The coverage hint keeps upstream's empty-composition message and joins
  every switched-on provider's hint otherwise.
- CHANGELOG, README and SECURITY keep both sides' entries.

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

package.json

@@ -163,6 +163,7 @@
     "./layers/vessels": "./src/layers/vessels/index.js",
     "./layers/earthquakes": "./src/layers/earthquakes/index.js",
     "./layers/recent-imagery": "./src/layers/recentImagery/index.js",
+    "./layers/recent-imagery/source": "./src/layers/recentImagery/source.js",
     "./layers/perimeters": "./src/layers/perimeters/index.js",
     "./sources/firms-csv": "./src/data/firmsCsv.js",
     "./layers/firms": "./src/layers/firms/index.js",
@@ -173,6 +174,7 @@
     "./layers/traffic": "./src/layers/traffic/index.js",
     "./layers/bikeshare": "./src/layers/bikeshare/index.js",
     "./layers/directions": "./src/layers/directions/index.js",
+    "./layers/directions/source": "./src/layers/directions/source.js",
     "./layers/cctv": "./src/layers/cctv/index.js",
     "./layers/alpr": "./src/layers/alpr/index.js",
     "./layers/radio": "./src/layers/radio/index.js",