feat: push marketplace URL to runtime; fix market client base race

- On connecting to the plugin runtime, push the configured space.url via the
  new SET_RUNTIME_CONFIG action so the runtime downloads plugins from the same
  Space, instead of relying on its own CLOUD_SERVICE_URL env/default. Wrapped
  in try/except so an older SDK without the action degrades gracefully.
- web: the plugin market fetched recommendation lists (and listings) via the
  sync cloud client before its baseURL was resolved from system info, so it
  hit the default space.langbot.app. Await getCloudServiceClient() before the
  initial fetches and for the recommendation list.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/langbot/pkg/plugin/handler.py

@@ -779,6 +779,16 @@ class RuntimeConnectionHandler(handler.Handler):
             timeout=10,
         )
 
+    async def set_runtime_config(self, cloud_service_url: str) -> dict[str, Any]:
+        """Push runtime configuration (e.g. marketplace URL) to the runtime."""
+        return await self.call_action(
+            LangBotToRuntimeAction.SET_RUNTIME_CONFIG,
+            {
+                'cloud_service_url': cloud_service_url,
+            },
+            timeout=10,
+        )
+
     async def install_plugin(
         self, install_source: str, install_info: dict[str, Any]
     ) -> typing.AsyncGenerator[dict[str, Any], None]: