feat: 完成后端服务核心业务逻辑实现

## 主要功能
- ✅ 用户认证模块 (登录/注册/JWT)
- ✅ 照片管理模块 (上传/查询/分页/搜索)
- ✅ 分类管理模块 (创建/查询/分页)
- ✅ 用户管理模块 (用户列表/分页查询)
- ✅ 健康检查接口

## 技术实现
- 基于 go-zero v1.8.0 标准架构
- Handler → Logic → Model 三层架构
- SQLite/PostgreSQL 数据库支持
- JWT 认证机制
- bcrypt 密码加密
- 统一响应格式
- 自定义模型方法 (分页/搜索)

## API 接口
- POST /api/v1/auth/login - 用户登录
- POST /api/v1/auth/register - 用户注册
- GET /api/v1/health - 健康检查
- GET /api/v1/photos - 照片列表
- POST /api/v1/photos - 上传照片
- GET /api/v1/categories - 分类列表
- POST /api/v1/categories - 创建分类
- GET /api/v1/users - 用户列表

## 配置完成
- 开发环境配置 (SQLite)
- 生产环境支持 (PostgreSQL)
- JWT 认证配置
- 文件上传配置
- Makefile 构建脚本

服务已验证可正常构建和启动。

backend/internal/model/photomodel_gen.go

@@ -0,0 +1,93 @@
+// Code generated by goctl. DO NOT EDIT.
+// versions:
+//  goctl version: 1.8.4
+
+package model
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/zeromicro/go-zero/core/stores/builder"
+	"github.com/zeromicro/go-zero/core/stores/sqlx"
+	"github.com/zeromicro/go-zero/core/stringx"
+)
+
+var (
+	photoFieldNames          = builder.RawFieldNames(&Photo{})
+	photoRows                = strings.Join(photoFieldNames, ",")
+	photoRowsExpectAutoSet   = strings.Join(stringx.Remove(photoFieldNames, "`id`", "`create_at`", "`create_time`", "`created_at`", "`update_at`", "`update_time`", "`updated_at`"), ",")
+	photoRowsWithPlaceHolder = strings.Join(stringx.Remove(photoFieldNames, "`id`", "`create_at`", "`create_time`", "`created_at`", "`update_at`", "`update_time`", "`updated_at`"), "=?,") + "=?"
+)
+
+type (
+	photoModel interface {
+		Insert(ctx context.Context, data *Photo) (sql.Result, error)
+		FindOne(ctx context.Context, id int64) (*Photo, error)
+		Update(ctx context.Context, data *Photo) error
+		Delete(ctx context.Context, id int64) error
+	}
+
+	defaultPhotoModel struct {
+		conn  sqlx.SqlConn
+		table string
+	}
+
+	Photo struct {
+		Id            int64          `db:"id"`
+		Title         string         `db:"title"`          // 照片标题
+		Description   sql.NullString `db:"description"`    // 照片描述
+		FilePath      string         `db:"file_path"`      // 原图路径
+		ThumbnailPath string         `db:"thumbnail_path"` // 缩略图路径
+		UserId        int64          `db:"user_id"`        // 用户ID
+		CategoryId    int64          `db:"category_id"`    // 分类ID
+		CreatedAt     time.Time      `db:"created_at"`
+		UpdatedAt     time.Time      `db:"updated_at"`
+	}
+)
+
+func newPhotoModel(conn sqlx.SqlConn) *defaultPhotoModel {
+	return &defaultPhotoModel{
+		conn:  conn,
+		table: "`photo`",
+	}
+}
+
+func (m *defaultPhotoModel) Delete(ctx context.Context, id int64) error {
+	query := fmt.Sprintf("delete from %s where `id` = ?", m.table)
+	_, err := m.conn.ExecCtx(ctx, query, id)
+	return err
+}
+
+func (m *defaultPhotoModel) FindOne(ctx context.Context, id int64) (*Photo, error) {
+	query := fmt.Sprintf("select %s from %s where `id` = ? limit 1", photoRows, m.table)
+	var resp Photo
+	err := m.conn.QueryRowCtx(ctx, &resp, query, id)
+	switch err {
+	case nil:
+		return &resp, nil
+	case sqlx.ErrNotFound:
+		return nil, ErrNotFound
+	default:
+		return nil, err
+	}
+}
+
+func (m *defaultPhotoModel) Insert(ctx context.Context, data *Photo) (sql.Result, error) {
+	query := fmt.Sprintf("insert into %s (%s) values (?, ?, ?, ?, ?, ?)", m.table, photoRowsExpectAutoSet)
+	ret, err := m.conn.ExecCtx(ctx, query, data.Title, data.Description, data.FilePath, data.ThumbnailPath, data.UserId, data.CategoryId)
+	return ret, err
+}
+
+func (m *defaultPhotoModel) Update(ctx context.Context, data *Photo) error {
+	query := fmt.Sprintf("update %s set %s where `id` = ?", m.table, photoRowsWithPlaceHolder)
+	_, err := m.conn.ExecCtx(ctx, query, data.Title, data.Description, data.FilePath, data.ThumbnailPath, data.UserId, data.CategoryId, data.Id)
+	return err
+}
+
+func (m *defaultPhotoModel) tableName() string {
+	return m.table
+}