feat: 实现后端多环境配置机制

- 使用 toml crate 替代 config crate 直接读取配置文件
- 创建 config/default.toml、config/development.toml、config/production.toml
- 重写 config.rs 支持多环境配置加载
- 增强 deploy.sh 支持 development/production 环境参数
- 更新 IMPROVEMENTS.md 标记环境区分完成

Cargo.toml

@@ -21,6 +21,7 @@ serde = { version = "1.0.219", features = ["derive"] }
 serde_json = "1.0.143"
 sqlx = { version = "0.8.6", features = ["runtime-tokio-rustls", "postgres", "chrono", "uuid"] }
 tokio = { version = "1", features = ["full"] }
+toml = "0.8"
 
 [dev-dependencies]
 tokio = { version = "1", features = ["full"] }