fix(app-iced, presenter): M114 r3 —— 登录成功提示走 i18n key+参数，离线名字提交判据与 host 同源

- 新增 Key::AccountLoginSucceeded（Signed in as {name} / 已登录 {name}）：
  presenter 不再拼「已登录：{name}」这类人类可读句子（复审 r1 P1-1 的收尾）
- valid_offline_name 从 host 搬到 dto（UI 与 host 共用的同一个判据），
  Form::offline_ready 改用它：按钮不再「亮着但必然失败」
- 视图模型测试：成功提示按 i18n 渲染进 on_screen；离线提交判据加「太短也拒绝」断言

crates/i18n/src/catalog/account.rs

@@ -90,6 +90,7 @@ macro_rules! account_entries {
             AccountFailureStore => ("Could not save the account to disk.", "账户没能写到磁盘上。"),
             AccountFailureOther => ("The sign-in failed. The full reason is in the launcher log.", "登录失败，完整原因在启动器日志里。"),
             AccountDeviceRequesting => ("Contacting Microsoft…", "正在联系微软…"),
+            AccountLoginSucceeded => ("Signed in as {name}", "已登录 {name}"),
             // ── 账户页横幅（添加/删除/切换的结果；页面上真实可见，不是 toast）
             AccountNoticeAdded => ("Added {name}", "已添加 {name}"),
             AccountNoticeRemoved => ("Removed {name}", "已删除 {name}"),

crates/i18n/src/catalog/golden.rs

@@ -370,6 +370,7 @@ pub(super) const GOLDEN: &[(&str, &str, &str)] = &[
     ("AccountFailureStore", "Could not save the account to disk.", "账户没能写到磁盘上。"),
     ("AccountFailureOther", "The sign-in failed. The full reason is in the launcher log.", "登录失败，完整原因在启动器日志里。"),
     ("AccountDeviceRequesting", "Contacting Microsoft…", "正在联系微软…"),
+    ("AccountLoginSucceeded", "Signed in as {name}", "已登录 {name}"),
     ("AccountNoticeAdded", "Added {name}", "已添加 {name}"),
     ("AccountNoticeRemoved", "Removed {name}", "已删除 {name}"),
     ("AccountNoticeSwitched", "{name} will be used for the next launch", "{name} 将作为下次启动的账户"),