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/services/ai_generator.py

@@ -0,0 +1,144 @@
+"""
+AI 生图服务
+支持双模型：SiliconFlow FLUX.1 [dev] 和 火山引擎 Seedream 4.5
+"""
+import os
+import uuid
+import logging
+import httpx
+from typing import Optional
+
+from ..config import settings
+from .config_service import get_ai_config
+
+logger = logging.getLogger(__name__)
+
+# 超时设置（秒）
+REQUEST_TIMEOUT = 90
+# 最大重试次数
+MAX_RETRIES = 3
+
+
+async def _call_siliconflow(prompt: str, size: int = 1024, ai_config: dict = None) -> str:
+    """
+    调用 SiliconFlow FLUX.1 [dev] 生图 API
+    
+    Returns:
+        远程图片 URL
+    """
+    cfg = ai_config or get_ai_config()
+    url = f"{cfg['SILICONFLOW_BASE_URL']}/images/generations"
+    headers = {
+        "Authorization": f"Bearer {cfg['SILICONFLOW_API_KEY']}",
+        "Content-Type": "application/json",
+    }
+    payload = {
+        "model": "black-forest-labs/FLUX.1-dev",
+        "prompt": prompt,
+        "image_size": f"{size}x{size}",
+        "num_inference_steps": 20,
+    }
+
+    async with httpx.AsyncClient(timeout=REQUEST_TIMEOUT) as client:
+        resp = await client.post(url, json=payload, headers=headers)
+        resp.raise_for_status()
+        data = resp.json()
+
+    # SiliconFlow 响应格式: {"images": [{"url": "https://..."}]}
+    images = data.get("images", [])
+    if not images:
+        raise ValueError("SiliconFlow 返回空图片列表")
+    return images[0]["url"]
+
+
+async def _call_seedream(prompt: str, size: int = 1024, ai_config: dict = None) -> str:
+    """
+    调用火山引擎 Seedream 4.5 生图 API
+    
+    Returns:
+        远程图片 URL
+    """
+    cfg = ai_config or get_ai_config()
+    url = f"{cfg['VOLCENGINE_BASE_URL']}/images/generations"
+    headers = {
+        "Authorization": f"Bearer {cfg['VOLCENGINE_API_KEY']}",
+        "Content-Type": "application/json",
+    }
+    payload = {
+        "model": "doubao-seedream-4.5-t2i-250528",
+        "prompt": prompt,
+        "size": f"{size}x{size}",
+        "response_format": "url",
+    }
+
+    async with httpx.AsyncClient(timeout=REQUEST_TIMEOUT) as client:
+        resp = await client.post(url, json=payload, headers=headers)
+        resp.raise_for_status()
+        data = resp.json()
+
+    # Seedream 响应格式: {"data": [{"url": "https://..."}]}
+    items = data.get("data", [])
+    if not items:
+        raise ValueError("Seedream 返回空图片列表")
+    return items[0]["url"]
+
+
+async def generate_image(prompt: str, model: Optional[str] = None) -> str:
+    """
+    统一生图接口，带重试机制
+    
+    Args:
+        prompt: 英文提示词
+        model: 模型名称 (flux-dev / seedream-4.5)，为空则使用配置默认值
+        
+    Returns:
+        远程图片 URL
+        
+    Raises:
+        Exception: 所有重试失败后抛出
+    """
+    ai_config = get_ai_config()
+    model = model or ai_config.get("AI_IMAGE_MODEL", "flux-dev")
+    size = ai_config.get("AI_IMAGE_SIZE", 1024)
+
+    last_error: Optional[Exception] = None
+    for attempt in range(1, MAX_RETRIES + 1):
+        try:
+            if model == "seedream-4.5":
+                image_url = await _call_seedream(prompt, size, ai_config)
+            else:
+                image_url = await _call_siliconflow(prompt, size, ai_config)
+            logger.info(f"AI 生图成功 (model={model}, attempt={attempt})")
+            return image_url
+        except Exception as e:
+            last_error = e
+            logger.warning(f"AI 生图失败 (model={model}, attempt={attempt}/{MAX_RETRIES}): {e}")
+            if attempt < MAX_RETRIES:
+                import asyncio
+                await asyncio.sleep(2 * attempt)  # 指数退避
+
+    raise RuntimeError(f"AI 生图在 {MAX_RETRIES} 次重试后仍然失败: {last_error}")
+
+
+async def download_and_save(image_url: str, save_path: str) -> str:
+    """
+    下载远程图片并保存到本地
+    
+    Args:
+        image_url: 远程图片 URL
+        save_path: 本地保存路径（如 uploads/designs/1001_效果图.png）
+        
+    Returns:
+        本地文件相对路径（以 / 开头，如 /uploads/designs/1001_效果图.png）
+    """
+    # 确保目录存在
+    os.makedirs(os.path.dirname(save_path), exist_ok=True)
+
+    async with httpx.AsyncClient(timeout=60, follow_redirects=True) as client:
+        resp = await client.get(image_url)
+        resp.raise_for_status()
+        with open(save_path, "wb") as f:
+            f.write(resp.content)
+
+    logger.info(f"图片已下载保存: {save_path}")
+    return f"/{save_path}"