feat(street-level): provider exports and a Mapillary Graph endpoint for hosts (#1324)

* feat(street-level): export the KartaView and Panoramax providers

A host that composes Street Level with its own provider list can already
import the Mapillary and Google Street View providers; KartaView and Panoramax
were reachable only through the default list, which needs a Mapillary source.
Exporting them lets a host offer the keyless providers without Mapillary.

* chore: changelog entry for the Street Level provider exports

* feat(street-level): send Mapillary Graph lookups to a source endpoint

A Mapillary source can take a graphEndpoint, a Graph API base that adds
the token itself. Its sequence lookups go there through the source's
transport, and the photo viewer uses MapillaryJS's stock GraphDataProvider
at that endpoint, so a host that proxies Mapillary needs no client token in
the page. Without it, behaviour is unchanged: direct Graph API calls with
the client token.

package.json

@@ -272,6 +272,8 @@
     "./layers/street-level/mapillary": "./src/layers/streetLevel/providers/mapillary/index.js",
     "./layers/street-level/mapillary/source": "./src/layers/streetLevel/providers/mapillary/source.js",
     "./layers/street-level/google": "./src/layers/streetLevel/providers/google/index.js",
+    "./layers/street-level/kartaview": "./src/layers/streetLevel/providers/kartaview/index.js",
+    "./layers/street-level/panoramax": "./src/layers/streetLevel/providers/panoramax/index.js",
     "./tools": "./src/tools/index.js",
     "./tools/mcp": "./src/tools/mcp/index.js",
     "./tools/panel": "./src/tools/panel.js",