feat(ai): 自由创作视频生成全量移植(/free-create)——Seedance 文/图生视频+按时长计费+人物素材库

后端:
- free_video.py: 提交/轮询/收藏/软删全链路,复用 AITask(新增 is_deleted/is_favorited, migration 0022)
- video_pricing.py: 按时长 token 计费(×1.10 buffer+clamp); video_errors.py 错误归一; media_probe.py 时长探测
- catalog/volcano: Seedance free-video 模型接入+seed(migration 0023)
- 素材库: FreeAssetGroup/FreeAsset(火山 Assets API 引用登记, migration 0009)+ 上传/轮询/删除接口
- settings: FREE_VIDEO_MAX_CONCURRENT 团队并发闸(默认3); CELERY_TASK_ALWAYS_EAGER 本地联调开关(生产恒关)
- 测试: test_free_video.py 新增; billing/products/projects tests 配套调整

前端:
- /free-create 页面+components/free-create/ 全套(输入栏/@mention 素材引用/生成卡/视频详情弹窗/素材库弹窗)
- api.ts/types.ts 扩展 free-video 与 free-assets 接口; 路由/侧边栏入口接入

bug/: 测试清单 (11)(12) 与截图归档

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/frontend/src/components/IconKitSvg.tsx

@@ -27,7 +27,8 @@ const iconPaths: Record<string, string> = {
   server: '<rect x="2" y="3" width="20" height="8" rx="2"/><rect x="2" y="13" width="20" height="8" rx="2"/><path d="M6 7h.01"/><path d="M6 17h.01"/>',
   gauge: '<path d="m12 14 4-4"/><path d="M3.34 19a10 10 0 1 1 17.32 0"/>',
   sliders: '<line x1="4" x2="4" y1="21" y2="14"/><line x1="4" x2="4" y1="10" y2="3"/><line x1="12" x2="12" y1="21" y2="12"/><line x1="12" x2="12" y1="8" y2="3"/><line x1="20" x2="20" y1="21" y2="16"/><line x1="20" x2="20" y1="12" y2="3"/><line x1="2" x2="6" y1="14" y2="14"/><line x1="10" x2="14" y1="8" y2="8"/><line x1="18" x2="22" y1="16" y2="16"/>',
-  logOut: '<path d="M9 21H5a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h4"/><path d="m16 17 5-5-5-5"/><path d="M21 12H9"/>'
+  logOut: '<path d="M9 21H5a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h4"/><path d="m16 17 5-5-5-5"/><path d="M21 12H9"/>',
+  film: '<rect x="3" y="3" width="18" height="18" rx="2"/><path d="M7 3v18"/><path d="M17 3v18"/><path d="M3 7.5h4"/><path d="M3 16.5h4"/><path d="M17 7.5h4"/><path d="M17 16.5h4"/><path d="M3 12h4"/><path d="M17 12h4"/>'
 };
 
 const iconAliases: Record<string, string> = {