fix(panel): streamline system settings and server creation

Use shared action buttons and default to the login space. Allow staff to save startup-only experience settings while running and request a durable restart through the existing operator flow.

Grant the API PVC list permission needed to detect retained worlds before server creation, and show internal failures with a request ID. Cover permission, maintenance, restart and UI behavior with regression checks.

internal/api/api.go

@@ -566,6 +566,7 @@ func (a *API) externalAPIRoutes() []apiRoute {
 		// (handlers_retire.go); owner/admin-gated inside the handlers.
 		{Method: "PUT", Pattern: "/api/v1/servers/{name}/retirement", h: a.handleRetire},
 		{Method: "DELETE", Pattern: "/api/v1/servers/{name}/retirement", h: a.handleCancelRetire},
+		{Method: "POST", Pattern: "/api/v1/servers/{name}/restart", h: a.handleRestart},
 		{Method: "GET", Pattern: "/api/v1/servers/{name}/status", h: a.handleStatus},
 		// Identity self-read (spec §14 tiering): the panel reads this once at boot to
 		// learn its own tier and decide which navigation surfaces to render. App-tier —