Add MailerSend and template-based email verification

Introduced support for MailerSend as an email provider alongside SMTP, with configuration options in settings. Added Jinja2-based multi-language email templates for verification emails, and refactored the email sending logic to use these templates and support language selection based on user country code. Updated related services and API endpoints to pass country code and handle new response formats. Added dependencies for Jinja2 and MailerSend.

app/service/mailersend_service.py

@@ -0,0 +1,87 @@
+"""
+MailerSend 邮件发送服务
+使用 MailerSend API 发送邮件
+"""
+
+from typing import Any
+
+from app.config import settings
+from app.log import logger
+
+from mailersend import EmailBuilder, MailerSendClient
+
+
+class MailerSendService:
+    """MailerSend 邮件发送服务"""
+
+    def __init__(self):
+        if not settings.mailersend_api_key:
+            raise ValueError("MailerSend API Key is required when email_provider is 'mailersend'")
+        if not settings.mailersend_from_email:
+            raise ValueError("MailerSend from email is required when email_provider is 'mailersend'")
+
+        self.client = MailerSendClient(api_key=settings.mailersend_api_key)
+        self.from_email = settings.mailersend_from_email
+        self.from_name = settings.from_name
+
+    async def send_email(
+        self,
+        to_email: str,
+        subject: str,
+        content: str,
+        html_content: str | None = None,
+        metadata: dict[str, Any] | None = None,
+    ) -> dict[str, str]:
+        """
+        使用 MailerSend 发送邮件
+
+        Args:
+            to_email: 收件人邮箱地址
+            subject: 邮件主题
+            content: 邮件纯文本内容
+            html_content: 邮件HTML内容（如果有）
+            metadata: 额外元数据（未使用）
+
+        Returns:
+            返回格式为 {'id': 'message_id'} 的字典
+        """
+        try:
+            _ = metadata  # 避免未使用参数警告
+
+            # 构建邮件
+            email_builder = EmailBuilder()
+            email_builder.from_email(self.from_email, self.from_name)
+            email_builder.to_many([{"email": to_email}])
+            email_builder.subject(subject)
+
+            # 优先使用 HTML 内容，否则使用纯文本
+            if html_content:
+                email_builder.html(html_content)
+            else:
+                email_builder.text(content)
+
+            email = email_builder.build()
+
+            # 发送邮件
+            response = self.client.emails.send(email)
+
+            # 从 APIResponse 中提取 message_id
+            message_id = getattr(response, "id", "") if response else ""
+            logger.info(f"Successfully sent email via MailerSend to {to_email}, message_id: {message_id}")
+            return {"id": message_id}
+
+        except Exception as e:
+            logger.error(f"Failed to send email via MailerSend: {e}")
+            return {"id": ""}
+
+
+# 全局 MailerSend 服务实例
+_mailersend_service: MailerSendService | None = None
+
+
+def get_mailersend_service() -> MailerSendService:
+    """获取或创建 MailerSend 服务实例"""
+    global _mailersend_service
+    if _mailersend_service is None:
+        _mailersend_service = MailerSendService()
+    return _mailersend_service