feat[Go]: implement Create-Chat/Session, Delete-Session (#16386)

### What problem does this PR solve?

As title:
implement:
```go
chats.POST("", r.chatHandler.Create)
chats.POST("/:chat_id/sessions", r.chatSessionHandler.CreateSession)
chats.DELETE("/:chat_id/sessions", r.chatSessionHandler.DeleteSessions)
```

bug fixed:

f80d4c7843/internal/handler/chat.go (L84)
↓
```go
result, err := h.chatService.ListChats(userID, "1", keywords, page, pageSize, orderby, desc)
```

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
- [x] Refactoring

internal/handler/chat.go

@@ -17,6 +17,7 @@
 package handler
 
 import (
+	"encoding/json"
 	"net/http"
 	"ragflow/internal/common"
 	"strconv"
@@ -81,7 +82,7 @@ func (h *ChatHandler) ListChats(c *gin.Context) {
 	}
 
 	// List chats - default to valid status "1" (same as Python StatusEnum.VALID.value)
-	result, err := h.chatService.ListChats(userID, keywords, "1", page, pageSize, orderby, desc)
+	result, err := h.chatService.ListChats(userID, "1", keywords, page, pageSize, orderby, desc)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{
 			"code":    500,
@@ -97,6 +98,46 @@ func (h *ChatHandler) ListChats(c *gin.Context) {
 	})
 }
 
+// Create creates a chat.
+// @Summary Create Chat
+// @Description Create a chat, aligned with Python POST /api/v1/chats.
+// @Tags chat
+// @Accept json
+// @Produce json
+// @Param request body service.CreateChatRequest true "chat configuration"
+// @Success 200 {object} map[string]interface{}
+// @Router /api/v1/chats [post]
+func (h *ChatHandler) Create(c *gin.Context) {
+	user, errorCode, errorMessage := GetUser(c)
+	if errorCode != common.CodeSuccess {
+		jsonError(c, errorCode, errorMessage)
+		return
+	}
+
+	var req map[string]interface{}
+	decoder := json.NewDecoder(c.Request.Body)
+	decoder.UseNumber()
+	if err := decoder.Decode(&req); err != nil {
+		jsonError(c, common.CodeArgumentError, err.Error())
+		return
+	}
+	if req == nil {
+		req = map[string]interface{}{}
+	}
+
+	result, code, err := h.chatService.Create(user.ID, req)
+	if err != nil {
+		jsonError(c, code, err.Error())
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{
+		"code":    common.CodeSuccess,
+		"data":    result,
+		"message": "success",
+	})
+}
+
 // ListChatsNext list chats with advanced filtering and pagination
 // @Summary List Chats Next
 // @Description Get list of chats with filtering, pagination and sorting (equivalent to list_dialogs_next)

internal/handler/chat_session.go

@@ -17,11 +17,13 @@
 package handler
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
 	"net/http"
 	"ragflow/internal/common"
+	"strings"
 
 	"github.com/gin-gonic/gin"
 
@@ -349,6 +351,98 @@ func (h *ChatSessionHandler) GetSession(c *gin.Context) {
 	jsonResponse(c, common.CodeSuccess, result, "success")
 }
 
+// CreateSession create a session in a dialog
+func (h *ChatSessionHandler) CreateSession(c *gin.Context) {
+	user, errorCode, errorMessage := GetUser(c)
+	if errorCode != common.CodeSuccess {
+		jsonError(c, errorCode, errorMessage)
+		return
+	}
+
+	userID := strings.TrimSpace(user.ID)
+	if userID == "" {
+		jsonError(c, common.CodeBadRequest, "user_id is required")
+		return
+	}
+
+	chatID := strings.TrimSpace(c.Param("chat_id"))
+	if chatID == "" {
+		jsonError(c, common.CodeBadRequest, "chat_id is required")
+		return
+	}
+
+	req := map[string]interface{}{}
+	if err := json.NewDecoder(c.Request.Body).Decode(&req); err != nil {
+		if errors.Is(err, io.EOF) {
+			req = map[string]interface{}{}
+		} else {
+			jsonError(c, common.CodeArgumentError, err.Error())
+			return
+		}
+	}
+	if req == nil {
+		req = map[string]interface{}{}
+	}
+
+	result, code, err := h.chatSessionService.CreateSession(userID, chatID, req)
+	if err != nil {
+		if code == common.CodeAuthenticationError {
+			jsonResponse(c, code, false, err.Error())
+			return
+		}
+		jsonError(c, code, err.Error())
+		return
+	}
+
+	jsonResponse(c, common.CodeSuccess, result, "success")
+}
+
+// DeleteSessions delete a session in a dialog
+func (h *ChatSessionHandler) DeleteSessions(c *gin.Context) {
+	user, errorCode, errorMessage := GetUser(c)
+	if errorCode != common.CodeSuccess {
+		jsonError(c, errorCode, errorMessage)
+		return
+	}
+
+	chatID := strings.TrimSpace(c.Param("chat_id"))
+	if chatID == "" {
+		jsonError(c, common.CodeBadRequest, "chat_id is required")
+		return
+	}
+
+	userID := strings.TrimSpace(user.ID)
+	if userID == "" {
+		jsonError(c, common.CodeBadRequest, "user_id is required")
+		return
+	}
+
+	req := map[string]interface{}{}
+	if err := json.NewDecoder(c.Request.Body).Decode(&req); err != nil {
+		if errors.Is(err, io.EOF) {
+			req = map[string]interface{}{}
+		} else {
+			jsonError(c, common.CodeArgumentError, err.Error())
+			return
+		}
+	}
+	if req == nil {
+		req = map[string]interface{}{}
+	}
+
+	result, message, code, err := h.chatSessionService.DeleteSessions(userID, chatID, req)
+	if err != nil {
+		if code == common.CodeAuthenticationError {
+			jsonResponse(c, code, false, err.Error())
+			return
+		}
+		jsonError(c, code, err.Error())
+		return
+	}
+
+	jsonResponse(c, common.CodeSuccess, result, message)
+}
+
 func (h *ChatSessionHandler) UpdateSession(c *gin.Context) {
 	user, errorCode, errorMessage := GetUser(c)
 	if errorCode != common.CodeSuccess {