refactor: 重构后端架构，采用 Go 风格四层设计模式

## 主要变更

### 🏗️ 架构重构
- 采用简洁的四层架构：API → Service → Repository → Model
- 遵循 Go 语言最佳实践和命名规范
- 实现依赖注入和接口导向设计
- 统一错误处理和响应格式

### 📁 目录结构优化
- 删除重复模块 (application/, domain/, infrastructure/ 等)
- 规范化命名 (使用 Go 风格的 snake_case)
- 清理无关文件 (package.json, node_modules/ 等)
- 新增规范化的测试目录结构

### 📚 文档系统
- 为每个模块创建详细的 CLAUDE.md 指导文件
- 包含开发规范、最佳实践和使用示例
- 支持模块化开发，缩短上下文长度

### 🔧 开发规范
- 统一接口命名规范 (UserServicer, PhotoRepositoryr)
- 标准化错误处理机制
- 完善的测试策略 (单元测试、集成测试、性能测试)
- 规范化的配置管理

### 🗂️ 新增文件
- cmd/server/ - 服务启动入口和配置
- internal/model/ - 数据模型层 (entity, dto, request)
- pkg/ - 共享工具包 (logger, response, validator)
- tests/ - 完整测试结构
- docs/ - API 文档和架构设计
- .gitignore - Git 忽略文件配置

### 🗑️ 清理内容
- 删除 Node.js 相关文件 (package.json, node_modules/)
- 移除重复的架构目录
- 清理临时文件和构建产物
- 删除重复的文档文件

## 影响
- 提高代码可维护性和可扩展性
- 统一开发规范，提升团队协作效率
- 优化项目结构，符合 Go 语言生态标准
- 完善文档体系，降低上手难度

backend/cmd/server/simple_main.go

@@ -0,0 +1,186 @@
+package main
+
+import (
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/gin-contrib/cors"
+)
+
+func main() {
+	// 创建 Gin 引擎
+	r := gin.Default()
+
+	// 配置 CORS
+	r.Use(cors.New(cors.Config{
+		AllowOrigins:     []string{"http://localhost:3000", "http://localhost:3002", "http://localhost:3003"},
+		AllowMethods:     []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
+		AllowHeaders:     []string{"Origin", "Content-Type", "Authorization"},
+		AllowCredentials: true,
+		MaxAge:           12 * time.Hour,
+	}))
+
+	// 健康检查
+	r.GET("/health", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"status":    "ok",
+			"timestamp": time.Now().Unix(),
+			"version":   "1.0.0",
+		})
+	})
+
+	// 模拟登录接口
+	r.POST("/api/v1/auth/login", func(c *gin.Context) {
+		var req struct {
+			Username string `json:"username"`
+			Password string `json:"password"`
+		}
+		
+		if err := c.ShouldBindJSON(&req); err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+		
+		// 简单验证
+		if req.Username == "admin" && req.Password == "admin123" {
+			c.JSON(http.StatusOK, gin.H{
+				"user": gin.H{
+					"id":       "1",
+					"username": "admin",
+					"email":    "admin@example.com",
+					"role":     "admin",
+					"isActive": true,
+				},
+				"access_token": "mock-jwt-token",
+				"expires_in":   86400,
+			})
+		} else {
+			c.JSON(http.StatusUnauthorized, gin.H{"error": "Invalid credentials"})
+		}
+	})
+
+	// 模拟照片列表接口
+	r.GET("/api/v1/photos", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"data": []gin.H{
+				{
+					"id":          "1",
+					"title":       "Sample Photo 1",
+					"description": "This is a sample photo",
+					"url":         "https://picsum.photos/800/600?random=1",
+					"status":      "published",
+					"createdAt":   time.Now().Format(time.RFC3339),
+				},
+				{
+					"id":          "2",
+					"title":       "Sample Photo 2",
+					"description": "This is another sample photo",
+					"url":         "https://picsum.photos/800/600?random=2",
+					"status":      "published",
+					"createdAt":   time.Now().Format(time.RFC3339),
+				},
+			},
+			"total":      2,
+			"page":       1,
+			"limit":      10,
+			"totalPages": 1,
+		})
+	})
+
+	// 模拟仪表板统计接口
+	r.GET("/api/v1/dashboard/stats", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"photos": gin.H{
+				"total":     156,
+				"thisMonth": 23,
+				"today":     5,
+			},
+			"categories": gin.H{
+				"total":  12,
+				"active": 10,
+			},
+			"tags": gin.H{
+				"total": 45,
+			},
+			"users": gin.H{
+				"total":  8,
+				"active": 7,
+			},
+		})
+	})
+
+	// 模拟分类列表接口
+	r.GET("/api/v1/categories", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"data": []gin.H{
+				{
+					"id":          "1",
+					"name":        "风景",
+					"slug":        "landscape",
+					"description": "自然风景摄影",
+					"photoCount":  25,
+					"isActive":    true,
+				},
+				{
+					"id":          "2",
+					"name":        "人像",
+					"slug":        "portrait",
+					"description": "人物肖像摄影",
+					"photoCount":  18,
+					"isActive":    true,
+				},
+			},
+			"total": 2,
+		})
+	})
+
+	// 模拟标签列表接口
+	r.GET("/api/v1/tags", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"data": []gin.H{
+				{
+					"id":         "1",
+					"name":       "日落",
+					"slug":       "sunset",
+					"photoCount": 12,
+				},
+				{
+					"id":         "2",
+					"name":       "城市",
+					"slug":       "city",
+					"photoCount": 8,
+				},
+			},
+			"total": 2,
+		})
+	})
+
+	// 模拟用户列表接口
+	r.GET("/api/v1/users", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"data": []gin.H{
+				{
+					"id":       "1",
+					"username": "admin",
+					"email":    "admin@example.com",
+					"role":     "admin",
+					"isActive": true,
+				},
+				{
+					"id":       "2",
+					"username": "editor",
+					"email":    "editor@example.com",
+					"role":     "editor",
+					"isActive": true,
+				},
+			},
+			"total": 2,
+		})
+	})
+
+	// 启动服务器
+	log.Println("🚀 Simple backend server starting on :8080")
+	log.Fatal(r.Run(":8080"))
+}