feat(cron): add automatic log cleanup with retention policy

Implement LogCleaner cron job to automatically clean up old log records
based on configurable retention period and maximum record count.

- Add LogCleaner with retention_days and max_records configuration
- Add EZ_LOG_RETENTION_DAYS and EZ_LOG_MAX_RECORDS environment variables
- Default to 30 days retention and 1,000,000 max records
- Include unit tests for log cleaner functionality

internal/config/config.go

@@ -42,6 +42,8 @@ type LogConfig struct {
 	BatchSize     int
 	FlushInterval time.Duration
 	QueueCapacity int
+	RetentionDays int
+	MaxRecords    int
 }
 
 type ModelRegistryConfig struct {
@@ -73,6 +75,8 @@ func Load() (*Config, error) {
 	v.SetDefault("log.batch_size", 10)
 	v.SetDefault("log.flush_ms", 1000)
 	v.SetDefault("log.queue_capacity", 10000)
+	v.SetDefault("log.retention_days", 30)
+	v.SetDefault("log.max_records", 1000000)
 	v.SetDefault("auth.jwt_secret", "change_me_in_production")
 	v.SetDefault("model_registry.enabled", false)
 	v.SetDefault("model_registry.refresh_seconds", 1800)
@@ -95,6 +99,8 @@ func Load() (*Config, error) {
 	_ = v.BindEnv("log.batch_size", "EZ_LOG_BATCH_SIZE")
 	_ = v.BindEnv("log.flush_ms", "EZ_LOG_FLUSH_MS")
 	_ = v.BindEnv("log.queue_capacity", "EZ_LOG_QUEUE")
+	_ = v.BindEnv("log.retention_days", "EZ_LOG_RETENTION_DAYS")
+	_ = v.BindEnv("log.max_records", "EZ_LOG_MAX_RECORDS")
 	_ = v.BindEnv("auth.jwt_secret", "EZ_JWT_SECRET")
 	_ = v.BindEnv("model_registry.enabled", "EZ_MODEL_REGISTRY_ENABLED")
 	_ = v.BindEnv("model_registry.refresh_seconds", "EZ_MODEL_REGISTRY_REFRESH_SECONDS")
@@ -137,6 +143,8 @@ func Load() (*Config, error) {
 			BatchSize:     v.GetInt("log.batch_size"),
 			FlushInterval: time.Duration(v.GetInt("log.flush_ms")) * time.Millisecond,
 			QueueCapacity: v.GetInt("log.queue_capacity"),
+			RetentionDays: v.GetInt("log.retention_days"),
+			MaxRecords:    v.GetInt("log.max_records"),
 		},
 		Auth: AuthConfig{
 			JWTSecret: v.GetString("auth.jwt_secret"),