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_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"