fix: 优化后端各模块 handler

- database_handler, knowledge_handler, model_handler
- neo4j_handler, sub_table_handler
- system_handler, upload_handler
- knowledge_service, upload_service

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/internal/handler/system_handler.go

@@ -14,7 +14,14 @@ func NewSystemHandler() *SystemHandler {
 	return &SystemHandler{}
 }
 
-// GetSystemInfo 获取系统信息
+// @Summary 获取系统信息
+// @Description 获取服务器系统信息（CPU、内存等）
+// @Tags 系统
+// @Accept json
+// @Produce json
+// @Success 200 {object} model.SystemInfo
+// @Failure 500 {object} map[string]string
+// @Router /system/info [get]
 func (h *SystemHandler) GetSystemInfo(c *gin.Context) {
 	info, err := getSystemInfo()
 	if err != nil {