feat: add dual-engine email service with aliyun smtp and resend routing

Route Chinese domains (edu.cn, qq.com, 163.com, etc.) via Aliyun SMTP
and international addresses via Resend API.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/config.go

@@ -16,6 +16,25 @@ type Config struct {
 	Mathpix   MathpixConfig     `mapstructure:"mathpix"`
 	BaiduOCR  BaiduOCRConfig    `mapstructure:"baidu_ocr"`
 	Google    GoogleOAuthConfig `mapstructure:"google"`
+	Email     EmailConfig       `mapstructure:"email"`
+}
+
+type EmailConfig struct {
+	FromName   string           `mapstructure:"from_name"`
+	FromAddr   string           `mapstructure:"from_addr"`
+	AliyunSMTP AliyunSMTPConfig `mapstructure:"aliyun_smtp"`
+	Resend     ResendEmailConfig `mapstructure:"resend"`
+}
+
+type AliyunSMTPConfig struct {
+	Host     string `mapstructure:"host"`
+	Port     int    `mapstructure:"port"`
+	Username string `mapstructure:"username"`
+	Password string `mapstructure:"password"`
+}
+
+type ResendEmailConfig struct {
+	APIKey string `mapstructure:"api_key"`
 }
 
 type BaiduOCRConfig struct {

config/config_dev.yaml

@@ -56,3 +56,14 @@ google:
   client_secret: "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"
   redirect_uri: "https://app.cloud.texpixel.com:10443/auth/google/callback"
   proxy: "http://localhost:7890"
+
+email:
+  from_name: "TexPixel Support"
+  from_addr: "support@texpixel.com"
+  aliyun_smtp:
+    host: "smtp.qiye.aliyun.com"
+    port: 465
+    username: "support@texpixel.com"
+    password: "8bPw2W9LlgHSTTfk"
+  resend:
+    api_key: "re_xxxxxxxxxxxx"

config/config_prod.yaml

@@ -56,3 +56,14 @@ google:
   client_secret: "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"
   redirect_uri: "https://texpixel.com/auth/google/callback"
   proxy: "http://100.115.184.74:7890"
+
+email:
+  from_name: "TexPixel Support"
+  from_addr: "support@texpixel.com"
+  aliyun_smtp:
+    host: "smtp.qiye.aliyun.com"
+    port: 465
+    username: "support@texpixel.com"
+    password: "8bPw2W9LlgHSTTfk"
+  resend:
+    api_key: "re_xxxxxxxxxxxx"