feat(auth): migrate Flutter IAuthPlatform to Next.js 16 SDK service layer

Adds the third-party social login SDK integration layer (Google + Facebook),
mirroring the Flutter `IAuthPlatform` interface from
`lib/data/services/auth/`. The platform produces identity tokens only; callers
use the existing `authRepository.googleLogin / facebookLogin /
facebookIdLogin` (already migrated) to complete the login.

Architecture (event-bridge pattern):
  - `IAuthPlatform` is plain TypeScript (no React dependency)
  - `WebAuthPlatform` dispatches DOM `CustomEvent`s; `AuthPlatformBridge`
    ("use client" component) hosts the React SDK hooks and resolves promises
  - `MockAuthPlatform` returns hardcoded tokens when
    `NEXT_PUBLIC_USE_MOCK_AUTH=true` (mirrors Dart `kDebugMode` branch)

SDK choices:
  - `@react-oauth/google@0.13.5` for Google
  - `@greatsumini/react-facebook-login@3.4.0` (maintained fork of
    archived `react-facebook`, React 19 compatible) for Facebook
  - For Google: uses raw GIS `google.accounts.id.initialize` + `prompt` API
    since `@react-oauth/google` does not expose an `id_token` flow variant
    (existing `GoogleLoginRequest.idToken` field expects JWT id_token)

Files added:
  - src/data/services/auth/{auth_platform,web_auth_platform,
    mock_auth_platform,auth_event_bridge,auth_bridge_component,
    initialize_google_auth,initialize_facebook_auth,global.d.ts,index}.ts(x)
  - src/data/schemas/auth/facebook_user_data.ts (Zod schema)
  - src/data/dto/auth/facebook_user_data.ts (DTO class)

Files modified:
  - package.json, pnpm-lock.yaml: added 2 deps
  - .env.example: 4 new NEXT_PUBLIC_* env vars
  - barrelsby.json: registered src/data/services[/auth] directories
  - implementation_plan.md: appended third-party auth section
  - src/data/dto/{auth,chat,metrics,user}/index.ts: regenerated barrels
  - src/data/schemas/{auth,chat,metrics,user}/index.ts: regenerated barrels

Files deleted:
  - src/data/storage/index.ts: pre-existing TS2308 conflict (sync + async
    `AuthStorage` both re-exported from auto-generated barrel; no consumer
    uses the barrel — all imports use direct paths)

Scope (per user direction):
  - Client SDK integration only; no React hook/context, no UI, no Apple
  - Platform produces tokens; caller drives `authRepository` / `authApi`
  - v1 single-popup semantics (concurrent popups overwrite)
  - Bridge component is code-ready but NOT mounted in
    `src/app/layout.tsx`; next-step UI migration wires the provider chain

Verified: `npx tsc --noEmit` (0 errors), `pnpm lint` (0 errors),
`pnpm build` (Next.js 16.2.7 + Turbopack compiled successfully).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/data/schemas/auth/facebook_user_data.ts

@@ -0,0 +1,17 @@
+/**
+ * Facebook 用户数据 schema
+ * 原始 Dart: FacebookUserData (lib/data/services/auth/auth_platform.dart)
+ *
+ * 字段对齐 Dart 端 `String?` 可空语义：缺字段时存 `null`。
+ */
+import { z } from "zod";
+
+export const FacebookUserDataSchema = z.object({
+  id: z.string().nullable().default(null),
+  name: z.string().nullable().default(null),
+  email: z.string().nullable().default(null),
+  pictureUrl: z.string().nullable().default(null),
+});
+
+export type FacebookUserDataInput = z.input<typeof FacebookUserDataSchema>;
+export type FacebookUserDataData = z.output<typeof FacebookUserDataSchema>;

src/data/schemas/auth/index.ts

@@ -0,0 +1,18 @@
+/**
+ * @file Automatically generated by barrelsby.
+ */
+
+export * from "./apple_login_request";
+export * from "./facebook_login_request";
+export * from "./facebook_user_data";
+export * from "./fb_id_login_request";
+export * from "./google_login_request";
+export * from "./guest_login_request";
+export * from "./guest_login_response";
+export * from "./login_request";
+export * from "./login_response";
+export * from "./logout_response";
+export * from "./refresh_token_request";
+export * from "./refresh_token_response";
+export * from "./register_request";
+export * from "./send_code_request";

src/data/schemas/chat/index.ts

@@ -0,0 +1,14 @@
+/**
+ * @file Automatically generated by barrelsby.
+ */
+
+export * from "./chat_history_response";
+export * from "./chat_message";
+export * from "./chat_send_response";
+export * from "./chat_sync_data";
+export * from "./chat_sync_request";
+export * from "./guest_chat_quota";
+export * from "./image_upload_response";
+export * from "./send_message_request";
+export * from "./stt_data";
+export * from "./sync_message";

src/data/schemas/index.ts

@@ -1,11 +1,10 @@
 /**
- * Schemas - 集中导出
- *
- * Zod schema + 类型（Source of Truth）
- * 原始 Dart: lib/data/models/
+ * @file Automatically generated by barrelsby.
  */
+
 export * from "./auth/apple_login_request";
 export * from "./auth/facebook_login_request";
+export * from "./auth/facebook_user_data";
 export * from "./auth/fb_id_login_request";
 export * from "./auth/google_login_request";
 export * from "./auth/guest_login_request";
@@ -17,7 +16,6 @@ export * from "./auth/refresh_token_request";
 export * from "./auth/refresh_token_response";
 export * from "./auth/register_request";
 export * from "./auth/send_code_request";
-
 export * from "./chat/chat_history_response";
 export * from "./chat/chat_message";
 export * from "./chat/chat_send_response";
@@ -28,10 +26,8 @@ export * from "./chat/image_upload_response";
 export * from "./chat/send_message_request";
 export * from "./chat/stt_data";
 export * from "./chat/sync_message";
-
 export * from "./metrics/app_event";
 export * from "./metrics/pwa_event";
-
 export * from "./user/avatar_data";
 export * from "./user/credits_data";
 export * from "./user/credits_history_data";

src/data/schemas/metrics/index.ts

@@ -0,0 +1,6 @@
+/**
+ * @file Automatically generated by barrelsby.
+ */
+
+export * from "./app_event";
+export * from "./pwa_event";

src/data/schemas/user/index.ts

@@ -0,0 +1,12 @@
+/**
+ * @file Automatically generated by barrelsby.
+ */
+
+export * from "./avatar_data";
+export * from "./credits_data";
+export * from "./credits_history_data";
+export * from "./personality_traits";
+export * from "./recent_memory";
+export * from "./update_profile_request";
+export * from "./user";
+export * from "./user_stats_response";