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/backend/apps/ai/tasks.py

@@ -50,3 +50,30 @@ def generate_triview_task(self, task_id: str) -> str:
     run_triview_task(task_id=task_id)
     return task_id
 
+
+@app.task(bind=True, max_retries=0)
+def poll_free_video_task(self, task_id: str, attempt: int = 0) -> str:
+    """自由创作视频·worker 兜底轮询:每 30s 一次自重排(不依赖 celery beat),
+    上限 60 次(≈30 分钟,足够 Seedance 5-10 分钟出片)。finalize 幂等(POSTPROCESSING 认领),
+    与前端主动 poll 并存不双扣。轮询本身出错不重试(max_retries=0),下一次自重排继续。"""
+    from apps.ai.free_video import finalize_free_video
+    from apps.ai.models import AITask
+
+    task = AITask.objects.select_related("model_config", "model_config__provider", "team").filter(id=task_id).first()
+    if task is None:
+        return task_id
+    try:
+        task = finalize_free_video(task=task)
+    except Exception:  # noqa: BLE001 — 单次轮询失败(网络抖动等)不终结任务,等下一轮
+        import logging
+
+        logging.getLogger(__name__).warning("poll_free_video_task %s attempt %s failed", task_id, attempt, exc_info=True)
+    # eager(本地联调/单测)下 apply_async 会内联立即执行,自重排=同步死循环 → 跳过,收尾交给前端主动 poll
+    from django.conf import settings as dj_settings
+
+    if getattr(dj_settings, "CELERY_TASK_ALWAYS_EAGER", False):
+        return task_id
+    if task.status in (AITask.Status.SUBMITTED, AITask.Status.POLLING) and attempt < 60:
+        poll_free_video_task.apply_async(args=[task_id, attempt + 1], countdown=30)
+    return task_id
+