refactor(app): provide sub-config structures from main config

Extract DatabaseConfig, RedisConfig, RustFSConfig, LogConfig, and EmailConfig
from the main Config to enable pkg/* package constructors to receive specific
config types by value, supporting the fx.Lifecycle OnStop hooks pattern.

internal/app/infra_module.go

@@ -20,6 +20,13 @@ import (
 // 每个需要资源释放的组件都通过 fx.Lifecycle 注册 OnStop 钩子，
 // 彻底替代 main.go 里分散的 defer xxx.Close()。
 var InfraModule = fx.Options(
+	// 顶层 Config 子结构 Provider：让 pkg/* 包的构造函数按值接收细分 Config
+	fx.Provide(func(c *config.Config) config.DatabaseConfig { return c.Database }),
+	fx.Provide(func(c *config.Config) config.RedisConfig { return c.Redis }),
+	fx.Provide(func(c *config.Config) config.RustFSConfig { return c.RustFS }),
+	fx.Provide(func(c *config.Config) config.LogConfig { return c.Log }),
+	fx.Provide(func(c *config.Config) config.EmailConfig { return c.Email }),
+
 	// Logger
 	fx.Provide(logger.New),