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.go

@@ -9,10 +9,35 @@ import (
 	"time"
 
 	"log/slog"
+	"gopkg.in/natefinch/lumberjack.v2"
 )
 
 var logger *slog.Logger
 
+// Config holds logging configuration
+type Config struct {
+	Level      string
+	Output     string // "stdout", "stderr", or file path
+	Rotation   bool   // enable file rotation
+	MaxSize    int    // MB
+	MaxBackups int
+	MaxAge     int    // days
+	Compress   bool
+}
+
+// DefaultConfig returns default logging configuration
+func DefaultConfig() Config {
+	return Config{
+		Level:      "INFO",
+		Output:     "stdout",
+		Rotation:   false,
+		MaxSize:    100,
+		MaxBackups: 3,
+		MaxAge:     7,
+		Compress:   true,
+	}
+}
+
 // sensitiveFields contains field names that should be sanitized in logs
 var sensitiveFields = []string{
 	"token",
@@ -35,14 +60,47 @@ func Init() {
 
 // InitWithLevel initializes the logger with specified level
 func InitWithLevel(level string) {
-	levelVar := parseLevel(level)
+	cfg := DefaultConfig()
+	cfg.Level = level
+	InitWithConfig(cfg)
+}
+
+// InitWithConfig initializes the logger with full configuration
+func InitWithConfig(cfg Config) {
+	levelVar := parseLevel(cfg.Level)
 
 	opts := &slog.HandlerOptions{
 		Level:       levelVar,
 		ReplaceAttr: sanitizeAttrs,
 	}
 
-	handler := slog.NewJSONHandler(os.Stdout, opts)
+	var handler slog.Handler
+	
+	switch cfg.Output {
+	case "stdout":
+		handler = slog.NewJSONHandler(os.Stdout, opts)
+	case "stderr":
+		handler = slog.NewJSONHandler(os.Stderr, opts)
+	default:
+		// File output with optional rotation
+		if cfg.Rotation {
+			lumberjackLogger := &lumberjack.Logger{
+				Filename:   cfg.Output,
+				MaxSize:    cfg.MaxSize,
+				MaxBackups: cfg.MaxBackups,
+				MaxAge:     cfg.MaxAge,
+				Compress:   cfg.Compress,
+			}
+			handler = slog.NewJSONHandler(lumberjackLogger, opts)
+		} else {
+			file, err := os.OpenFile(cfg.Output, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
+			if err != nil {
+				panic(err)
+			}
+			handler = slog.NewJSONHandler(file, opts)
+		}
+	}
+	
 	logger = slog.New(handler)
 	slog.SetDefault(logger)
 }