feat(client): C 端 1-2 账号链路（邮箱登录/注册 + 令牌与 401 + 匿名/登录分叉）

为什么：客户端此前完全没有账号概念（mine 页的"登录"只是本地 demo 开关），
而受限动作（收藏/评论）要对到具体账号。本批把账号链路接上，为后续互动、进度同步、下载打底。

- AuthApi + AuthController + AuthSessionStore：注册/登录/登出/刷新，令牌与设备号存 shared_preferences
  （用 SharedPreferencesAsync，与 engagement 仓库同一套 API）
- ApiClient：统一带 Authorization 与 X-Device-Id；401 自动刷新一次并重试，刷新失败清登录态走 onUnauthorized
- 登录/注册页（pages/auth，沿用 binding/logic/view 与现有视觉）：邮箱格式、密码 8-64 位含字母数字本地先校验，
  错误提示走 l10n；登录/注册一键切换
- 匿名/登录分叉：首页、发现、详情保持匿名可看；收藏/点赞等受限动作走 ensureSignedIn() 弹底部提示引导登录
- mine 页展示真实账号（昵称 + uid），拿不到才回落到演示文案
- 测试：新增 auth 控制器（注册落盘/401 刷新重试/刷新失败清会话/登出）与登录页（校验/切换）用例；
  widget_test 改为预置本地会话（账号不再是本地开关）；修掉 playback 用例对 host 大小写的环境依赖断言

门禁：flutter analyze 0 问题；flutter test 148 全过。

lib/l10n/app_zh.arb

@@ -91,6 +91,8 @@
   "lockedBody": "完成商店与服务端验单配置后才能解锁。本演示目前不处理付款。",
   "playbackError": "此视频暂时无法播放。",
   "catalogError": "剧目列表加载失败。",
+  "detailError": "剧集信息加载失败。",
+  "noMediaNotice": "该剧集还没有可播放的片源。",
   "noStories": "暂无剧目。",
   "retry": "重试",
   "backToSeries": "返回剧集详情",
@@ -125,5 +127,53 @@
   "continueWatchingHeading": "继续观看",
   "preferencesHeading": "偏好设置",
   "brandMark": "NONTONKI · 演示",
-  "shareFooter": "Nontonki 演示"
+  "shareFooter": "Nontonki 演示",
+  "shortsTab": "短剧",
+  "myListTab": "片单",
+  "watchFull": "看全集",
+  "swipeForNext": "上滑看下一部",
+  "clearScreen": "清屏",
+  "exitClearScreen": "退出清屏",
+  "logIn": "登录",
+  "logInHint": "登录后保存金币和片单",
+  "rewards": "奖励",
+  "forYou": "为你推荐",
+  "hot": "热门",
+  "newest": "最新",
+  "favorite": "收藏",
+  "myAccount": "我的账户",
+  "coins": "金币",
+  "topUpWallet": "充值",
+  "vipMembership": "会员",
+  "notActive": "未开通",
+  "joinVip": "开通会员",
+  "earnRewards": "赚奖励",
+  "freeBonus": "领免费奖励",
+  "watchHistory": "观看历史",
+  "settings": "设置",
+  "signOut": "退出登录",
+  "mockUserName": "Vicky sheng",
+  "mockUserId": "ID: M1CZWVYE",
+  "mockNotice": "当前是示例数据。",
+  "topBadge": "TOP 1",
+  "signIn": "登录",
+  "signUp": "注册",
+  "authSignInTitle": "欢迎回来",
+  "authSignUpTitle": "创建账号",
+  "authSubtitle": "用邮箱和密码登录。",
+  "authEmailLabel": "邮箱",
+  "authPasswordLabel": "密码",
+  "authPasswordHint": "至少 8 位，需包含字母和数字",
+  "authEmailRequired": "请输入邮箱",
+  "authEmailInvalid": "邮箱格式不正确",
+  "authPasswordRequired": "请输入密码",
+  "authPasswordLength": "密码长度需在 8-64 位之间",
+  "authPasswordWeak": "密码需同时包含字母和数字",
+  "authNetworkError": "网络异常，请稍后重试",
+  "authSwitchToSignUp": "还没有账号？去注册",
+  "authSwitchToSignIn": "已有账号？去登录",
+  "authGateTitle": "登录后可继续",
+  "authGateMessage": "收藏、评论等操作需要登录。",
+  "authGateAction": "去登录",
+  "cancel": "暂不"
 }