feat: 强化多视角图片一致性 + 修复下载逻辑 + 技术文档

- 新增品类专属背面/侧面描述(BACK_VIEW_HINTS/SIDE_VIEW_HINTS)
- 强化一致性前缀策略，按视角定制相机位置描述
- 更新视角映射提示词为纯摄影术语
- 修复前端下载逻辑：改用fetch直接下载当前视角图片
- HTTPS改HTTP修复外网URL访问
- 新增多视角一致性与3D视频生成技术文档

backend/uvicorn.log

@@ -69,3 +69,14 @@ INFO:     127.0.0.1:63569 - "GET /uploads/models/506909359d6c45fe9e43108ee7765a9
 INFO:     127.0.0.1:63575 - "POST /api/designs/27/generate-video?force=true HTTP/1.1" 200 OK
 INFO:     127.0.0.1:63785 - "GET /uploads/videos/6ed3f33421a44876b303c7671c1597d5.mp4 HTTP/1.1" 200 OK
 INFO:     127.0.0.1:63846 - "GET /uploads/videos/6ed3f33421a44876b303c7671c1597d5.mp4 HTTP/1.1" 200 OK
+WARNING:  StatReload detected changes in 'app/routers/designs.py'. Reloading...
+INFO:     Shutting down
+INFO:     Waiting for application shutdown.
+INFO:     Application shutdown complete.
+INFO:     Finished server process [64861]
+👋 应用已关闭
+INFO:     Started server process [65045]
+INFO:     Waiting for application startup.
+INFO:     Application startup complete.
+✅ 上传目录已准备: uploads
+INFO:     127.0.0.1:64149 - "GET /uploads/videos/6ed3f33421a44876b303c7671c1597d5.mp4 HTTP/1.1" 304 Not Modified