feat(log): B-03 日志轮转配置 - 添加 lumberjack 支持

- 添加 lumberjack.v2 依赖实现日志轮转
- 支持配置文件输出（stdout/stderr/file）
- 支持文件轮转（100MB/3备份/7天/压缩）
- 添加 Config 结构体灵活配置
- 添加完整测试用例

测试验证：
- TestInitWithConfig PASS
- TestInitWithConfigFileOutput PASS
- TestDefaultConfig PASS
- 全量日志测试通过

internal/log/log_test.go

@@ -2,6 +2,7 @@ package log
 
 import (
 	"log/slog"
+	"os"
 	"testing"
 )
 
@@ -130,3 +131,59 @@ func TestRequestLogger(t *testing.T) {
 		t.Error("RequestLogger should not return nil")
 	}
 }
+
+func TestInitWithConfig(t *testing.T) {
+	// Test with stdout output
+	cfg := DefaultConfig()
+	cfg.Output = "stdout"
+	cfg.Level = "DEBUG"
+	InitWithConfig(cfg)
+	
+	if logger == nil {
+		t.Error("logger should not be nil after InitWithConfig")
+	}
+}
+
+func TestInitWithConfigFileOutput(t *testing.T) {
+	// Test with file output (no rotation)
+	tmpFile := t.TempDir() + "/test.log"
+	cfg := DefaultConfig()
+	cfg.Output = tmpFile
+	cfg.Rotation = false
+	InitWithConfig(cfg)
+	
+	Info("test message for file")
+	
+	// Verify file was created
+	if _, err := os.Stat(tmpFile); os.IsNotExist(err) {
+		t.Errorf("log file %s should exist", tmpFile)
+	}
+}
+
+func TestDefaultConfig(t *testing.T) {
+	cfg := DefaultConfig()
+	
+	if cfg.Level != "INFO" {
+		t.Errorf("default Level = %s, want INFO", cfg.Level)
+	}
+	
+	if cfg.Output != "stdout" {
+		t.Errorf("default Output = %s, want stdout", cfg.Output)
+	}
+	
+	if cfg.MaxSize != 100 {
+		t.Errorf("default MaxSize = %d, want 100", cfg.MaxSize)
+	}
+	
+	if cfg.MaxBackups != 3 {
+		t.Errorf("default MaxBackups = %d, want 3", cfg.MaxBackups)
+	}
+	
+	if cfg.MaxAge != 7 {
+		t.Errorf("default MaxAge = %d, want 7", cfg.MaxAge)
+	}
+	
+	if !cfg.Compress {
+		t.Error("default Compress should be true")
+	}
+}