refactor(auth): unify Facebook and Google login into AuthPlatform class

Replace the separate FacebookLogin and GoogleLogin classes with a single
AuthPlatform class that takes a provider name ("facebook" | "google") as a
constructor argument. This consolidates duplicate OAuth sign-in logic behind
one entry point while preserving the existing NextAuth flow.

- Add new src/lib/auth/auth_platform.ts exporting AuthPlatform and
  AuthProvider type
- Update auth-facebook-panel.tsx and splash-button.tsx to use the new API
- Rename initialContext → initialState in the auth machine for consistency
- Update inline docs and comments to reference AuthPlatform

No behavioral change for end users; both providers still route through
NextAuth's signIn() with the same callbacks and cookies.

src/stores/auth/auth-machine.ts

@@ -1,189 +0,0 @@
-/**
- * Auth 状态机（XState v5）
- *
- * 原始 Dart: lib/ui/auth/bloc/auth_bloc.dart + auth_state.dart + auth_event.dart
- *
- * 本轮迁移：社交登录改由 NextAuth 处理（`@/lib/auth/nextauth`），状态机仅保留
- * 邮箱注册/登录 + 通用 reset 事件。社交登录走 `new GoogleLogin().signIn()` /
- * `new FacebookLogin().signIn()`。
- */
-import { setup, fromPromise, assign } from "xstate";
-
-import type { LoginType } from "@/models/auth/login-type";
-import { authRepository } from "@/data/repositories/auth_repository";
-import { AuthStorage } from "@/data/storage/auth/auth_storage";
-import { Result } from "@/utils/result";
-
-import { AuthContext, initialContext } from "./auth-context";
-import type { AuthEvent } from "./auth-events";
-
-// 重新导出 Context / Event 类型，保持 machine 文件的公共 API 不变
-export type { AuthContext } from "./auth-context";
-export { initialContext } from "./auth-context";
-export type { AuthEvent } from "./auth-events";
-
-// ============================================================
-// Helpers
-// ============================================================
-async function readGuestId(): Promise<string | undefined> {
-  const r = await AuthStorage.getInstance().getDeviceId();
-  if (r.success && r.data != null) {
-    return r.data;
-  }
-  return undefined;
-}
-
-// ============================================================
-// Actors（异步服务）
-// ============================================================
-// 邮箱登录 actor 仅调 authRepository.emailLogin 拿业务 token。
-// 本轮起不再调 /api/auth/marker 写 cookie（统一迁到 NextAuth session
-// cookie 检测，邮箱登录 proxy 行为在后续轮恢复）。
-
-const emailLoginActor = fromPromise<LoginType, { email: string; password: string }>(
-  async ({ input }) => {
-    const guestId = await readGuestId();
-    const result = await authRepository.emailLogin({ ...input, guestId });
-    if (Result.isErr(result)) throw result.error;
-    return "email" as LoginType;
-  },
-);
-
-const emailRegisterThenLoginActor = fromPromise<
-  LoginType,
-  { email: string; password: string; username: string; confirmPassword: string }
->(async ({ input }) => {
-  const guestId = await readGuestId();
-
-  const registerResult = await authRepository.register({ ...input, guestId });
-  if (Result.isErr(registerResult)) throw registerResult.error;
-
-  // 注册后自动登录（对齐 Dart 行为）
-  const loginResult = await authRepository.emailLogin({
-    email: input.email,
-    password: input.password,
-    guestId,
-  });
-  if (Result.isErr(loginResult)) throw loginResult.error;
-  return "email" as LoginType;
-});
-
-// ============================================================
-// Machine
-// ============================================================
-export const authMachine = setup({
-  types: {
-    context: {} as AuthContext,
-    events: {} as AuthEvent,
-  },
-  actors: {
-    emailLogin: emailLoginActor,
-    emailRegisterThenLogin: emailRegisterThenLoginActor,
-  },
-}).createMachine({
-  id: "auth",
-  initial: "idle",
-  context: initialContext,
-  states: {
-    idle: {
-      on: {
-        AuthPanelModeChanged: {
-          actions: assign({
-            authPanelMode: ({ event }) => event.mode,
-            errorMessage: null,
-          }),
-        },
-        AuthModeChanged: {
-          actions: assign({
-            authMode: ({ event }) => event.mode,
-            errorMessage: null,
-          }),
-        },
-        AuthFormCleared: {
-          actions: assign({
-            email: "",
-            password: "",
-            username: "",
-            confirmPassword: "",
-            errorMessage: null,
-          }),
-        },
-        AuthReset: {
-          actions: assign(() => initialContext),
-        },
-        AuthEmailLoginSubmitted: "loadingEmailLogin",
-        AuthEmailRegisterSubmitted: "loadingEmailRegister",
-        // 社交登录已迁移到 NextAuth + GoogleLogin / FacebookLogin 类
-        // 状态机保留事件以兼容旧调用方（实际不再触发）
-        AuthGoogleLoginSubmitted: {},
-        AuthFacebookLoginSubmitted: {},
-        AuthAppleLoginSubmitted: {
-          actions: assign({
-            errorMessage: "Apple login not implemented",
-          }),
-        },
-      },
-    },
-
-    loadingEmailLogin: {
-      invoke: {
-        src: "emailLogin",
-        input: ({ event }) => {
-          if (event.type !== "AuthEmailLoginSubmitted")
-            return { email: "", password: "" };
-          return { email: event.email, password: event.password };
-        },
-        onDone: {
-          target: "success",
-          actions: assign({
-            loginType: ({ event }) => event.output,
-            errorMessage: null,
-          }),
-        },
-        onError: {
-          target: "idle",
-          actions: assign({
-            errorMessage: ({ event }) =>
-              event.error instanceof Error ? event.error.message : String(event.error),
-          }),
-        },
-      },
-    },
-
-    loadingEmailRegister: {
-      invoke: {
-        src: "emailRegisterThenLogin",
-        input: ({ event }) => {
-          if (event.type !== "AuthEmailRegisterSubmitted")
-            return { email: "", password: "", username: "", confirmPassword: "" };
-          return {
-            email: event.email,
-            password: event.password,
-            username: event.username,
-            confirmPassword: event.confirmPassword,
-          };
-        },
-        onDone: {
-          target: "success",
-          actions: assign({
-            loginType: ({ event }) => event.output,
-            errorMessage: null,
-          }),
-        },
-        onError: {
-          target: "idle",
-          actions: assign({
-            errorMessage: ({ event }) =>
-              event.error instanceof Error ? event.error.message : String(event.error),
-          }),
-        },
-      },
-    },
-
-    success: {
-      // 终态：业务层通过 state.matches("success") 判断
-    },
-  },
-});
-
-export type AuthMachine = typeof authMachine;