feat(ai): 支持双模型多视角AI设计生图与后台管理系统

- 实现AI多视角设计图生成功能，支持6个可选设计参数配置
- 集成SiliconFlow FLUX.1与火山引擎Seedream 4.5双模型切换
- 构建专业中文转英文prompt系统，提升AI生成质量
- 前端设计预览支持多视角切换与视角指示器展示
- 增加多视角设计图片DesignImage模型关联及存储
- 后端设计服务异步调用AI接口，失败时降级生成mock图
- 新增管理员后台管理路由及完整的权限校验机制
- 实现后台模块：仪表盘、系统配置、用户/品类/设计管理
- 配置数据库系统配置表，支持动态AI配置及热更新
- 增加用户管理员标识字段，管理后台登录鉴权支持
- 更新API接口支持多视角设计参数及后台管理接口
- 优化设计删除逻辑，删除多视角相关图片文件
- 前端新增管理后台页面与路由，布局样式独立分离
- 更新环境变量增加AI模型相关Key与参数配置说明
- 引入httpx异步HTTP客户端用于AI接口调用及图片下载
- README文档完善AI多视角生图与后台管理详细功能与流程说明

backend/app/schemas/admin.py

@@ -0,0 +1,173 @@
+"""
+管理后台相关 Pydantic Schemas
+"""
+from pydantic import BaseModel, Field
+from datetime import datetime
+from typing import Optional, List
+
+
+# ============ 系统配置 ============
+class SystemConfigItem(BaseModel):
+    """单个配置项"""
+    config_key: str
+    config_value: Optional[str] = None
+    description: Optional[str] = None
+    config_group: str = "general"
+    is_secret: str = "N"
+    updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class SystemConfigUpdate(BaseModel):
+    """批量更新配置"""
+    configs: dict = Field(..., description="键值对: {config_key: config_value}")
+
+
+class SystemConfigResponse(BaseModel):
+    """配置列表响应"""
+    items: List[SystemConfigItem]
+
+
+# ============ 用户管理 ============
+class AdminUserResponse(BaseModel):
+    """管理端用户信息"""
+    id: int
+    username: str
+    nickname: Optional[str] = None
+    phone: Optional[str] = None
+    is_admin: bool = False
+    created_at: datetime
+    design_count: int = 0
+
+    class Config:
+        from_attributes = True
+
+
+class AdminUserListResponse(BaseModel):
+    """用户列表响应"""
+    items: List[AdminUserResponse]
+    total: int
+    page: int
+    page_size: int
+
+
+class AdminSetAdmin(BaseModel):
+    """设置管理员"""
+    is_admin: bool
+
+
+# ============ 品类管理 ============
+class CategoryCreate(BaseModel):
+    """创建品类"""
+    name: str = Field(..., max_length=50)
+    icon: Optional[str] = Field(None, max_length=255)
+    sort_order: int = 0
+    flow_type: str = Field("full", max_length=20)
+
+
+class CategoryUpdate(BaseModel):
+    """更新品类"""
+    name: Optional[str] = Field(None, max_length=50)
+    icon: Optional[str] = Field(None, max_length=255)
+    sort_order: Optional[int] = None
+    flow_type: Optional[str] = Field(None, max_length=20)
+
+
+class SubTypeCreate(BaseModel):
+    """创建子类型"""
+    category_id: int
+    name: str = Field(..., max_length=50)
+    description: Optional[str] = Field(None, max_length=255)
+    preview_image: Optional[str] = Field(None, max_length=255)
+    sort_order: int = 0
+
+
+class SubTypeUpdate(BaseModel):
+    """更新子类型"""
+    name: Optional[str] = Field(None, max_length=50)
+    description: Optional[str] = Field(None, max_length=255)
+    preview_image: Optional[str] = Field(None, max_length=255)
+    sort_order: Optional[int] = None
+
+
+class ColorCreate(BaseModel):
+    """创建颜色"""
+    category_id: int
+    name: str = Field(..., max_length=50)
+    hex_code: Optional[str] = Field(None, max_length=10)
+    sort_order: int = 0
+
+
+class ColorUpdate(BaseModel):
+    """更新颜色"""
+    name: Optional[str] = Field(None, max_length=50)
+    hex_code: Optional[str] = Field(None, max_length=10)
+    sort_order: Optional[int] = None
+
+
+# ============ 设计管理 ============
+class AdminDesignListResponse(BaseModel):
+    """管理端设计列表"""
+    items: list
+    total: int
+    page: int
+    page_size: int
+
+
+# ============ 提示词管理 ============
+class PromptTemplateItem(BaseModel):
+    """提示词模板"""
+    id: Optional[int] = None
+    template_key: str
+    template_value: str
+    description: Optional[str] = None
+    updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class PromptTemplateUpdate(BaseModel):
+    """更新提示词模板"""
+    template_value: str
+    description: Optional[str] = None
+
+
+class PromptMappingItem(BaseModel):
+    """提示词映射"""
+    id: Optional[int] = None
+    mapping_type: str
+    cn_key: str
+    en_value: str
+    sort_order: int = 0
+    updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class PromptMappingCreate(BaseModel):
+    """创建提示词映射"""
+    mapping_type: str
+    cn_key: str
+    en_value: str
+    sort_order: int = 0
+
+
+class PromptMappingUpdate(BaseModel):
+    """更新提示词映射"""
+    cn_key: Optional[str] = None
+    en_value: Optional[str] = None
+    sort_order: Optional[int] = None
+
+
+# ============ 仪表盘 ============
+class DashboardStats(BaseModel):
+    """仪表盘统计"""
+    total_users: int
+    total_designs: int
+    total_categories: int
+    today_designs: int
+    today_users: int