feat(api): add Lovart-style project and agent thread endpoints

Add canva/canda-compatible routes for lightweight project open/save and
agent thread history:
- POST /canva/project/queryProject, saveProject
- POST /canva/agent/queryAgentLastThread, agentThreadList
- GET /canda/chat-history, /canda/thread/status

Canvas save now accepts a compressed SHAKKERDATA:// snapshot payload,
preserves connections, and returns a SaveProject response; blank
successful image nodes are backfilled from generated artifacts. Frontend
designGateway adopts the new save/query flow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/logic/agent_thread_list_logic.go

@@ -0,0 +1,93 @@
+// Code scaffolded by goctl. Safe to edit.
+// goctl 1.10.1
+
+package logic
+
+import (
+	"context"
+
+	"img_infinite_canvas/internal/svc"
+	"img_infinite_canvas/internal/types"
+
+	"github.com/zeromicro/go-zero/core/logx"
+)
+
+type AgentThreadListLogic struct {
+	logx.Logger
+	ctx    context.Context
+	svcCtx *svc.ServiceContext
+}
+
+func NewAgentThreadListLogic(ctx context.Context, svcCtx *svc.ServiceContext) *AgentThreadListLogic {
+	return &AgentThreadListLogic{
+		Logger: logx.WithContext(ctx),
+		ctx:    ctx,
+		svcCtx: svcCtx,
+	}
+}
+
+func (l *AgentThreadListLogic) AgentThreadList(req *types.AgentThreadListRequest) (resp *types.LovartAgentThreadListResponse, err error) {
+	project, err := l.svcCtx.DesignService.GetProject(l.ctx, req.ProjectId)
+	if err != nil {
+		return nil, err
+	}
+	threads, err := l.svcCtx.DesignService.AgentThreads(l.ctx, req.ProjectId)
+	if err != nil {
+		return nil, err
+	}
+
+	page := req.Page
+	if page <= 0 {
+		page = 1
+	}
+	pageSize := req.PageSize
+	if pageSize <= 0 {
+		pageSize = 100
+	}
+	if pageSize > 100 {
+		pageSize = 100
+	}
+	total := int64(len(threads))
+	start := (page - 1) * pageSize
+	if start > total {
+		start = total
+	}
+	end := start + pageSize
+	if end > total {
+		end = total
+	}
+	items := make([]types.LovartAgentThreadSummary, 0, end-start)
+	for index, thread := range threads[start:end] {
+		var cover *string
+		if thread.CoverImageURL != "" {
+			value := thread.CoverImageURL
+			cover = &value
+		}
+		items = append(items, types.LovartAgentThreadSummary{
+			Id:              start + int64(index) + 1,
+			UserId:          project.UserID,
+			ProjectId:       req.ProjectId,
+			AgentThreadId:   thread.AgentThreadID,
+			ThreadIdType:    thread.ThreadIDType,
+			Title:           "",
+			Text:            thread.Text,
+			CoverImageUrl:   cover,
+			FileType:        nil,
+			UpdateTimestamp: thread.UpdateTimestamp,
+			Source:          1,
+		})
+	}
+	return &types.LovartAgentThreadListResponse{
+		Code: 0,
+		Msg:  nil,
+		Data: types.LovartAgentThreadListData{
+			Page:     page,
+			Total:    total,
+			PageSize: pageSize,
+			Data:     items,
+			UserIp:   "",
+			TraceId:  "",
+			HasMore:  end < total,
+		},
+	}, nil
+}