feat(admin-web/login): replace default test credentials with remembered login

Why: showing the seed admin account on the login screen is unsafe for production deployments.
How to apply: store identifier/password in localStorage when "记住密码" is checked, restore them on mount, and drop the demo credentials panel.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/i18n/messages/en-US.ts

@@ -95,8 +95,8 @@ const enUS = {
     email: "Email",
     loginIdentifier: "Phone / Email",
     password: "Password",
-    defaultTestAccount: "Default account",
-    defaultTestPassword: "Default password",
+    rememberPassword: "Remember password",
+    forgotPassword: "Forgot password",
   },
   membershipBlocked: {
     eyebrow: "Access Paused",

apps/admin-web/src/i18n/messages/zh-CN.ts

@@ -96,8 +96,8 @@ const zhCN = {
     email: "邮箱",
     loginIdentifier: "手机号 / 邮箱",
     password: "密码",
-    defaultTestAccount: "默认测试账号",
-    defaultTestPassword: "默认测试密码",
+    rememberPassword: "记住密码",
+    forgotPassword: "忘记密码",
   },
   membershipBlocked: {
     eyebrow: "访问已暂停",