refactor: 配置安全加固-从TOML移除密钥+去除死代码+统一端口

P0: 从config/production.toml和config/development.toml移除wechat_secret/jwt_secret
    这些密钥现在仅通过.env(EnvironmentFile)加载，不再进入Git历史
    config.rs: 新增直接环境变量名回退(JWT_SECRET而非仅APP_JWT_SECRET)
    
P1: - 移除config.rs中的server_ports字段(死代码,未被任何代码使用)
    - 简化main.rs端口fallback: 生产环境仅4433,开发环境仅8080/3000
    - .env.example版本号0.2.3→0.3.0
    
Docs: - AGENTS.md测试域名xmclassmate.top/dev→dev.xmclassmate.top

src/main.rs

@@ -183,10 +183,10 @@ async fn main() -> std::io::Result<()> {
     info!("Attempting to start server...");
 
     let is_production = std::env::var("APP_ENV").unwrap_or_else(|_| "development".into()) == "production";
-    let ports = if is_production {
-        vec![4433, 8443, 8080, 3000, 8000, 8888]
+    let ports: Vec<u16> = if is_production {
+        vec![4433]
     } else {
-        vec![8080, 3000, 8000, 8888, 4433, 8443]
+        vec![8080, 3000]
     };
     let mut server: Option<
         Pin<Box<dyn std::future::Future<Output = std::io::Result<()>> + Unpin>>,