feat(devices): P1 设备注册打通 —— 登录/注册即写 devices 表

后端:auth.Service 加 DeviceMeta + DeviceRegistrar 接口(consumer-side 解耦),
Login/Register 成功签发后 best-effort 注册设备(不强制设备上限,避免免费档重装
churn 锁死用户);handler 加 device 请求体;main 用 authDeviceRegistrar 适配
devices.Service 注入;normalizePlatform 加 linux。
客户端:新 device_identity.dart(SecureKV 接缝 + 稳定 UUIDv4 device_id 持久化 +
名称/平台/版本);弃用硬编码 'mac-001';auth_api login/register + connect 携带
device 元数据。加 uuid + device_info_plus 依赖。
测试:auth 设备注册(触发/best-effort/空 meta) + device_identity(生成/持久/
读失败不重生成/UUIDv4 形态);normalizePlatform linux=true。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/widgets/auth_screen.dart

@@ -10,6 +10,7 @@ import '../l10n/app_text.dart';
 import '../pangolin_theme.dart';
 import '../services/api_config.dart';
 import '../services/auth_api.dart';
+import '../services/device_identity.dart';
 import '../state/auth_provider.dart';
 import 'pangolin_button.dart';
 import 'pangolin_icons.dart';
@@ -100,10 +101,12 @@ class _AuthScreenState extends ConsumerState<AuthScreen>
   Future<void> _doRegister() async {
     setState(() { _loading = true; _errorZh = null; });
     try {
+      final device = (await ref.read(deviceIdentityProvider).meta()).toJson();
       final tokens = await _api.register(
         email: _email.text.trim(),
         code: _code.text.trim(),
         password: _pw.text,
+        device: device,
       );
       await ref.read(tokenStoreProvider).saveLastEmail(_email.text.trim());
       await ref.read(authProvider.notifier).saveTokens(tokens);
@@ -116,9 +119,11 @@ class _AuthScreenState extends ConsumerState<AuthScreen>
   Future<void> _doLogin() async {
     setState(() { _loading = true; _errorZh = null; });
     try {
+      final device = (await ref.read(deviceIdentityProvider).meta()).toJson();
       final tokens = await _api.login(
         email: _email.text.trim(),
         password: _pw.text,
+        device: device,
       );
       await ref.read(tokenStoreProvider).saveLastEmail(_email.text.trim());
       await ref.read(authProvider.notifier).saveTokens(tokens);