fix: handle HTTPError in JetBrainsPluginClient initialization

When the JetBrains plugin service returns HTTP 503 error, the client
now gracefully handles it by setting _plugin_version and _project_root
to None, allowing the port scanning logic to continue trying other ports.

Fixes #962

src/serena/tools/jetbrains_plugin_client.py

@@ -93,7 +93,7 @@ class JetBrainsPluginClient(ToStringMixin):
             status_response: PluginStatusDTO = cast(jb.PluginStatusDTO, self._make_request("GET", "/status"))
             self._project_root = status_response["project_root"]
             self._plugin_version = Version(status_response["plugin_version"])
-        except ConnectionError:
+        except (ConnectionError, requests.exceptions.HTTPError):
             self._project_root = None
             self._plugin_version = None