feat(ai): 升级AI生图模型及多视角一致性支持

- 将默认AI生图模型升级为flux-dev及seedream-5.0版本
- SiliconFlow模型由FLUX.1-dev切换为Kolors，优化调用参数和返回值
- 火山引擎Seedream升级至5.0 lite版本，支持多视角参考图传入
- 设计图片字段由字符串改为Text扩展URL长度限制
- 设计图下载支持远程URL重定向和本地文件兼容
- 生成AI图片时多视角保持风格一致，SiliconFlow复用seed，Seedream传参考图
- 后台配置界面更改模型名称及价格显示，新增API Key状态检测
- 前端照片下载从链接改为按钮，远程文件新窗口打开
- 设计相关接口支持较长请求超时，下载走API路径无/api前缀
- 前端页面兼容驼峰与下划线格式URL参数识别
- 用户中心设计图下载支持本地文件Token授权下载
- 初始化数据库新增完整表结构与约束，适配新版设计业务逻辑

frontend/src/views/UserCenter.vue

@@ -174,6 +174,7 @@ import { useUserStore } from '@/stores/user'
 import { useDesignStore, type Design } from '@/stores/design'
 import { updateProfileApi, changePasswordApi } from '@/api/auth'
 import { getDesignDownloadUrl } from '@/api/design'
+import request from '@/api/request'
 
 const router = useRouter()
 const userStore = useUserStore()
@@ -282,18 +283,34 @@ const handleCardClick = (design: Design) => {
 }
 
 // Handle download
-const handleDownload = (design: Design) => {
+const handleDownload = async (design: Design) => {
   if (!design.image_url) {
     ElMessage.warning('暂无可下载的图片')
     return
   }
-  const link = document.createElement('a')
-  link.href = getDesignDownloadUrl(design.id)
-  link.download = `design_${design.id}.png`
-  link.target = '_blank'
-  document.body.appendChild(link)
-  link.click()
-  document.body.removeChild(link)
+  // 远程 URL 直接新窗口打开
+  const imgUrl = design.image_url
+  if (imgUrl.startsWith('http')) {
+    window.open(imgUrl, '_blank')
+    return
+  }
+  // 本地文件通过 axios 携带 Token 下载
+  try {
+    const response = await request.get(getDesignDownloadUrl(design.id), {
+      responseType: 'blob'
+    }) as any
+    const blob = new Blob([response], { type: 'image/png' })
+    const url = window.URL.createObjectURL(blob)
+    const link = document.createElement('a')
+    link.href = url
+    link.download = `design_${design.id}.png`
+    document.body.appendChild(link)
+    link.click()
+    document.body.removeChild(link)
+    window.URL.revokeObjectURL(url)
+  } catch {
+    ElMessage.error('下载失败，请重试')
+  }
 }
 
 // Handle delete