fix(auth): surface validation errors in email login/register forms

Validation failure was previously silent — the form's submit() returned
without dispatching or showing anything on screen, so users could not tell
why the login/register button appeared to do nothing.

Changes:
- Add validationError local state in EmailLoginForm and EmailRegisterForm
- Display first validation error via AuthErrorMessage, prioritised over
  the server's globalError (validation errors feel more immediate)
- Clear validation error on field change (standard "error fades as you
  fix it" UX) — implemented as onChange handlers, not useEffect, to
  avoid React's cascading-render anti-pattern
- Add observability to the entire email flow (was previously silent end
  to end): form submit ENTRY, validator rejection, actor ENTRY, actor
  DONE — mirrors the logging style already used by guestLoginActor
- Add entry: assign({ errorMessage: null }) to loadingEmailLogin and
  loadingEmailRegister so stale errors clear on transition into the
  loading state (matches loadingGuestLogin)

src/models/auth/login-status.ts

@@ -1,17 +1,10 @@
 /**
  * 登录状态枚举
- *
- * 原始 Dart: lib/ui/auth/bloc/auth_state.dart 的 `LoginType` 枚举（v7.0 新增）。
- *
- * 2025-XX 改造：语义从"登录方式"扩展为"当前登录状态"——
- * 包含 notLoggedIn / guest / 各 OAuth provider 登录后态。
- *
- * 字段命名（state）从 `loginType` 改为 `loginStatus`，更贴合语义。
  */
 export const LoginStatus = {
   /** 未登录（默认初值） */
   NotLoggedIn: "notLoggedIn",
-  /** 游客登录（无需账号，10 轮免费消息） */
+  /** 游客登录 */
   Guest: "guest",
   /** Facebook OAuth 登录 */
   Facebook: "facebook",