feat(server): workflow log-writer registry, retention setting, sweeper

server/internal/api/handlers.go

@@ -450,14 +450,15 @@ func getSettings(c *gin.Context) {
 
 func saveSettings(c *gin.Context) {
 	var body struct {
-		Alerts models.AlertSettings `json:"alerts"`
-		Email  models.EmailSettings `json:"email"`
+		Alerts                   models.AlertSettings `json:"alerts"`
+		Email                    models.EmailSettings `json:"email"`
+		WorkflowLogRetentionDays *int                 `json:"workflow_log_retention_days"`
 	}
 	if err := c.ShouldBindJSON(&body); err != nil {
 		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 		return
 	}
-	if err := services.SaveSettings(body.Alerts, body.Email); err != nil {
+	if err := services.SaveSettings(body.Alerts, body.Email, body.WorkflowLogRetentionDays); err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 		return
 	}