refactor(config): decouple logging config and update readme

Refactors internal/config to use logging.Config directly, removing duplication. Updates README.md to reference configuration documentation.

internal/config/config.go

@@ -8,18 +8,14 @@ import (
 	"strings"
 	"time"
 
+	"github.com/placeholder/golang-template/internal/logging"
 	"gopkg.in/yaml.v3"
 )
 
 // Config holds the application configuration.
 type Config struct {
-	Logging LoggingConfig `yaml:"logging"`
-	Server  ServerConfig  `yaml:"server"`
-}
-
-// LoggingConfig holds logging-specific configuration.
-type LoggingConfig struct {
-	Level string `yaml:"level"`
+	Logging logging.Config `yaml:"logging"`
+	Server  ServerConfig   `yaml:"server"`
 }
 
 // ServerConfig holds server-specific configuration.