feat(auth): implement Resend email quota and rate limit protection

Track Resend API usage via response headers to prevent quota exhaustion
Block auth requests with 503 when email delivery limits are reached

system-wordings.ts

@@ -998,7 +998,8 @@ export const systemWordingMessages = {
       verifyEmailFirst: 'Please complete email verification first',
       invalidResetToken: 'The password reset link is invalid or expired',
       currentPasswordInvalid: 'Current password is incorrect',
-      invalidReferralCode: 'Referral code is invalid'
+      invalidReferralCode: 'Referral code is invalid',
+      emailDeliveryUnavailable: 'Email delivery is temporarily unavailable. Please try again later.'
     },
     validation: {
       nameRequired: 'Name is required',
@@ -2072,7 +2073,8 @@ export const systemWordingMessages = {
         verifyEmailFirst: '请先完成邮箱验证',
         invalidResetToken: '密码重置链接无效或已过期',
         currentPasswordInvalid: '当前密码不正确',
-        invalidReferralCode: '邀请码无效'
+        invalidReferralCode: '邀请码无效',
+        emailDeliveryUnavailable: '邮件发送暂时不可用，请稍后再试。'
       },
       validation: {
         nameRequired: '请输入名称',