feat: Implement thread-safe account and statistics management and integrate proxy support for all external requests.

config.toml.example

@@ -30,3 +30,6 @@ domains = ["example.com"]
 # base_url = "https://mail2.example.com/"
 # api_token = "your_api_token_here"
 # domains = ["domain2.com", "domain3.com"]
+
+# --- 代理配置 ---
+# 代理从 proxy.txt 文件加载，格式: host:port:user:pass（每行一个）