refactor(auth): extract helpers and actors out of auth-machine

Move the file-local Helpers block (readGuestId) to auth-helpers.ts and the
Actors block (authRepo + 7 fromPromise actors) to auth-actors.ts. Public API
(authMachine, AuthEvent, AuthState, initialState, AuthMachine) is unchanged;
auth-context.tsx and the barrel index.ts need no edits.

src/stores/auth/auth-helpers.ts

@@ -0,0 +1,15 @@
+/**
+ * Auth 状态机：Helpers
+ *
+ * 状态机内复用的小函数 —— 独立成文件便于测试 / 复用。
+ */
+import { AuthStorage } from "@/data/storage/auth/auth_storage";
+
+/** 从本地存储读 guest deviceId；读不到 / 失败时返回 undefined（不抛）。 */
+export async function readGuestId(): Promise<string | undefined> {
+  const r = await AuthStorage.getInstance().getDeviceId();
+  if (r.success && r.data != null) {
+    return r.data;
+  }
+  return undefined;
+}