feat[Go]: implement /system/stats and refactor /system/config/log (#15407)

### What problem does this PR solve?

As title

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Refactoring

internal/handler/stats.go

@@ -0,0 +1,69 @@
+//
+//  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+
+package handler
+
+import (
+	"errors"
+	"net/http"
+	"time"
+
+	"ragflow/internal/common"
+	"ragflow/internal/service"
+
+	"github.com/gin-gonic/gin"
+)
+
+// GetStats returns API conversation statistics for the current user's tenant.
+func (h *SystemHandler) GetStats(c *gin.Context) {
+	user, errorCode, errorMessage := GetUser(c)
+	if errorCode != common.CodeSuccess {
+		jsonError(c, errorCode, errorMessage)
+		return
+	}
+
+	now := time.Now()
+	fromDate := c.DefaultQuery("from_date", now.AddDate(0, 0, -7).Format("2006-01-02 00:00:00"))
+	toDate := c.DefaultQuery("to_date", now.Format("2006-01-02 15:04:05"))
+	if len(toDate) == 10 {
+		toDate += " 23:59:59"
+	}
+
+	var source *string
+	if _, ok := c.GetQuery("canvas_id"); ok {
+		agentSource := "agent"
+		source = &agentSource
+	}
+
+	stats, err := h.systemService.GetStats(user.ID, fromDate, toDate, source)
+	if err != nil {
+		code := common.CodeExceptionError
+		if errors.Is(err, service.ErrTenantNotFound) {
+			code = common.CodeDataError
+		}
+		c.JSON(http.StatusOK, gin.H{
+			"code":    code,
+			"message": err.Error(),
+		})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{
+		"code":    common.CodeSuccess,
+		"message": "success",
+		"data":    stats,
+	})
+}

internal/handler/system.go

@@ -164,44 +164,46 @@ func (h *SystemHandler) GetVersion(c *gin.Context) {
 
 // GetLogLevel returns the current log level
 func (h *SystemHandler) GetLogLevel(c *gin.Context) {
-	level := common.GetLevel()
 	c.JSON(http.StatusOK, gin.H{
 		"code":    0,
 		"message": "success",
-		"data":    gin.H{"level": level},
+		"data":    common.GetLogLevels(),
 	})
 }
 
 // SetLogLevelRequest set log level request
 type SetLogLevelRequest struct {
-	Level string `json:"level" binding:"required"`
+	PkgName string `json:"pkg_name" binding:"required"`
+	Level   string `json:"level" binding:"required"`
 }
 
 // SetLogLevel sets the log level at runtime
 func (h *SystemHandler) SetLogLevel(c *gin.Context) {
 	var req SetLogLevelRequest
 	if err := c.ShouldBindJSON(&req); err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{
-			"code":    400,
-			"message": "level is required",
+		c.JSON(http.StatusOK, gin.H{
+			"code":    common.CodeDataError,
+			"message": "pkg_name and level are required",
 		})
 		return
 	}
 
-	if err := common.SetLevel(req.Level); err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{
-			"code":    400,
-			"message": err.Error(),
+	if err := common.SetPackageLogLevel(req.PkgName, req.Level); err != nil {
+		c.JSON(http.StatusOK, gin.H{
+			"code":    common.CodeDataError,
+			"message": "Invalid log level: " + req.Level,
 		})
 		return
 	}
 
 	config := server.GetConfig()
-	config.Log.Level = req.Level
+	if req.PkgName == "root" && config != nil {
+		config.Log.Level = common.GetLevel()
+	}
 
 	c.JSON(http.StatusOK, gin.H{
 		"code":    0,
-		"message": "Log level updated successfully",
-		"data":    gin.H{"level": req.Level},
+		"message": "success",
+		"data":    gin.H{"pkg_name": req.PkgName, "level": req.Level},
 	})
 }