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/airshelf/settings/base.py

@@ -162,6 +162,9 @@ CACHES = {
 
 CELERY_BROKER_URL = env("CELERY_BROKER_URL", "redis://127.0.0.1:6379/1")
 CELERY_RESULT_BACKEND = env("CELERY_RESULT_BACKEND", "redis://127.0.0.1:6379/2")
+# 本地端到端联调开关:true = 任务同进程内联执行,不碰共享 Redis 队列(线上 worker 拓扑不受影响)。
+# 生产/集群绝不开;test.py 恒为 True。自重排类任务(poll_free_video_task)在 eager 下会跳过重排防递归。
+CELERY_TASK_ALWAYS_EAGER = str(env("CELERY_TASK_ALWAYS_EAGER", "false")).lower() == "true"
 CELERY_TASK_ACKS_LATE = True
 CELERY_TASK_REJECT_ON_WORKER_LOST = True
 CELERY_WORKER_PREFETCH_MULTIPLIER = 1
@@ -229,6 +232,9 @@ PROVIDER_API_VERSIONS = {
     "yunqi": env("YUNQI_API_VERSION", "2025-04-01-preview"),
 }
 
+# 自由创作视频:团队在途任务并发上限(视频长时高价,限并发同时压 web 慢调用敞口)
+FREE_VIDEO_MAX_CONCURRENT = int(env("FREE_VIDEO_MAX_CONCURRENT", "3"))
+
 # 火山引擎人像素材库审核(真人资产绿/红盾)· AK/SK 暂借 AirDrama 已邀测账号,张业昌待换成 AirShelf 自有
 ASSETS_API = {
     "access_key": env("ASSETS_API_ACCESS_KEY", ""),