更新项目架构与存储适配器，添加用户认证功能

本次提交包含以下主要更改：
1. 更新 `.gitignore` 文件，添加对 `node_modules` 和环境变量文件的忽略。
2. 修改 `.gitmodules` 文件，替换为新的子模块 `cloudflare-worker`。
3. 新增 `ARCHITECTURE.md` 和 `PROJECT_REFACTOR_PLAN.md` 文档，详细描述项目架构和改造计划。
4. 实现用户认证功能，添加 GitHub OAuth 处理逻辑，支持 JWT 生成与解析。
5. 引入新的存储接口 `CanvasStore`，并实现相应的存储逻辑，支持用户画布的增删改查。
6. 更新 `main.go` 文件，整合新的认证与存储逻辑，优化路由设置。

这些更改旨在提升项目的可扩展性与用户体验，支持多用户环境下的画布管理与存储。

stores/memory/store.go

@@ -0,0 +1,166 @@
+package memory
+
+import (
+	"context"
+	"excalidraw-complete/core"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/oklog/ulid/v2"
+	"github.com/sirupsen/logrus"
+)
+
+var (
+	savedDocuments = make(map[string]core.Document)
+	// savedCanvases is a map where the key is userID, and the value is another map
+	// where the key is canvasID and the value is the canvas itself.
+	savedCanvases = make(map[string]map[string]*core.Canvas)
+	mu            sync.RWMutex
+)
+
+// memStore implements both DocumentStore and CanvasStore for in-memory storage.
+type memStore struct{}
+
+// NewStore creates a new in-memory store.
+func NewStore() *memStore {
+	return &memStore{}
+}
+
+// FindID retrieves a document by its ID. Part of the DocumentStore interface.
+func (s *memStore) FindID(ctx context.Context, id string) (*core.Document, error) {
+	mu.RLock()
+	defer mu.RUnlock()
+
+	log := logrus.WithField("document_id", id)
+	if val, ok := savedDocuments[id]; ok {
+		log.Info("Document retrieved successfully")
+		return &val, nil
+	}
+	log.WithField("error", "document not found").Warn("Document with specified ID not found")
+	return nil, fmt.Errorf("document with id %s not found", id)
+}
+
+// Create stores a new document. Part of the DocumentStore interface.
+func (s *memStore) Create(ctx context.Context, document *core.Document) (string, error) {
+	mu.Lock()
+	defer mu.Unlock()
+
+	id := ulid.Make().String()
+	savedDocuments[id] = *document
+	log := logrus.WithFields(logrus.Fields{
+		"document_id": id,
+		"data_length": len(document.Data.Bytes()),
+	})
+	log.Info("Document created successfully")
+
+	return id, nil
+}
+
+// List returns metadata for all canvases owned by a user. Part of the CanvasStore interface.
+func (s *memStore) List(ctx context.Context, userID string) ([]*core.Canvas, error) {
+	mu.RLock()
+	defer mu.RUnlock()
+
+	userCanvases, ok := savedCanvases[userID]
+	if !ok {
+		return []*core.Canvas{}, nil // No canvases for this user, return empty slice
+	}
+
+	canvases := make([]*core.Canvas, 0, len(userCanvases))
+	for _, canvas := range userCanvases {
+		// Important: create a copy without the large `Data` field for the list view
+		listCanvas := &core.Canvas{
+			ID:        canvas.ID,
+			UserID:    canvas.UserID,
+			Name:      canvas.Name,
+			CreatedAt: canvas.CreatedAt,
+			UpdatedAt: canvas.UpdatedAt,
+		}
+		canvases = append(canvases, listCanvas)
+	}
+
+	logrus.WithField("user_id", userID).Infof("Listed %d canvases", len(canvases))
+	return canvases, nil
+}
+
+// Get returns a single canvas by its ID, ensuring it belongs to the user. Part of the CanvasStore interface.
+func (s *memStore) Get(ctx context.Context, userID, id string) (*core.Canvas, error) {
+	mu.RLock()
+	defer mu.RUnlock()
+
+	log := logrus.WithFields(logrus.Fields{"user_id": userID, "canvas_id": id})
+
+	userCanvases, ok := savedCanvases[userID]
+	if !ok {
+		log.Warn("User has no canvases")
+		return nil, fmt.Errorf("canvas with id %s not found for user %s", id, userID)
+	}
+
+	canvas, ok := userCanvases[id]
+	if !ok {
+		log.Warn("Canvas not found for user")
+		return nil, fmt.Errorf("canvas with id %s not found for user %s", id, userID)
+	}
+
+	log.Info("Canvas retrieved successfully")
+	return canvas, nil
+}
+
+// Save creates or updates a canvas for a user. Part of the CanvasStore interface.
+func (s *memStore) Save(ctx context.Context, canvas *core.Canvas) error {
+	mu.Lock()
+	defer mu.Unlock()
+
+	log := logrus.WithFields(logrus.Fields{"user_id": canvas.UserID, "canvas_id": canvas.ID})
+
+	if canvas.UserID == "" {
+		return fmt.Errorf("UserID cannot be empty")
+	}
+
+	userCanvases, ok := savedCanvases[canvas.UserID]
+	if !ok {
+		userCanvases = make(map[string]*core.Canvas)
+		savedCanvases[canvas.UserID] = userCanvases
+	}
+
+	if canvas.ID == "" {
+		return fmt.Errorf("Canvas ID cannot be empty for save operation")
+	}
+
+	now := time.Now()
+	if existingCanvas, exists := userCanvases[canvas.ID]; exists {
+		canvas.CreatedAt = existingCanvas.CreatedAt
+		canvas.UpdatedAt = now
+	} else {
+		canvas.CreatedAt = now
+		canvas.UpdatedAt = now
+	}
+
+	userCanvases[canvas.ID] = canvas
+	log.Info("Canvas saved successfully")
+	return nil
+}
+
+// Delete removes a canvas, ensuring it belongs to the user. Part of the CanvasStore interface.
+func (s *memStore) Delete(ctx context.Context, userID, id string) error {
+	mu.Lock()
+	defer mu.Unlock()
+
+	log := logrus.WithFields(logrus.Fields{"user_id": userID, "canvas_id": id})
+
+	userCanvases, ok := savedCanvases[userID]
+	if !ok {
+		log.Warn("User has no canvases to delete from")
+		return fmt.Errorf("user %s has no canvases", userID)
+	}
+
+	if _, ok := userCanvases[id]; !ok {
+		log.Warn("Canvas not found for deletion")
+		return fmt.Errorf("canvas with id %s not found for user %s", id, userID)
+	}
+
+	delete(userCanvases, id)
+	log.Info("Canvas deleted successfully")
+	return nil
+}