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/routes/route-config.ts

@@ -27,6 +27,7 @@ export type Page =
   | "team"
   | "messages"
   | "assetFactory"
+  | "freeCreate"
   | "imageOptimize"
   | "modelPhoto"
   | "modelPhotoDemoA"
@@ -92,6 +93,7 @@ export const routeLabels: Record<Page, string> = {
   team: "团队",
   messages: "消息",
   assetFactory: "图片工具",
+  freeCreate: "自由创作",
   imageOptimize: "图片创作",
   modelPhoto: "模特上身图",
   modelPhotoDemoA: "模特图方案 A",
@@ -151,6 +153,7 @@ export function resolveRoute(): ResolvedRoute {
   if (path === "/team") return { page: "team", authMode: "login", hash };
   if (path === "/messages") return { page: "messages", authMode: "login", hash };
   if (path === "/asset-factory") return { page: "assetFactory", authMode: "login", hash };
+  if (path === "/free-create") return { page: "freeCreate", authMode: "login", hash };
   if (path === "/image-optimize") return { page: "imageOptimize", authMode: "login", hash };
   if (path === "/model-photo") return { page: "modelPhoto", authMode: "login", hash };
   if (path === "/model-photo/demo-a") return { page: "modelPhotoDemoA", authMode: "login", hash };
@@ -190,6 +193,8 @@ export function pathForPage(page: Page, options: NavigateOptions = {}) {
       return "/messages";
     case "assetFactory":
       return "/asset-factory";
+    case "freeCreate":
+      return "/free-create";
     case "imageOptimize":
       return "/image-optimize";
     case "modelPhoto":