Improve loading speed of desktop app (#4865)

# Description of Changes
Improve loading speed of desktop app by loading a default config until
the backend has spawned.

frontend/src/core/services/backendReadinessGuard.ts

@@ -0,0 +1,7 @@
+/**
+ * Default backend readiness guard (web builds do not need to wait for
+ * anything outside the browser, so we always report ready).
+ */
+export async function ensureBackendReady(): Promise<boolean> {
+  return true;
+}