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/providers/volcano.py

@@ -192,12 +192,19 @@ class VolcanoArkProvider:
         resolution: str = "720p",
         reference_images: list[str] | None = None,
         generate_audio: bool = True,
+        content_items: list[dict[str, Any]] | None = None,
+        seed: int | None = None,
+        search_mode: str = "off",
     ) -> dict[str, Any]:
         if not self.api_key:
             raise ValueError("VOLCANO_ARK_API_KEY is not configured")
         content: list[dict[str, Any]] = [{"type": "text", "text": prompt}]
-        for image_url in reference_images or []:
-            content.append({"type": "image_url", "image_url": {"url": image_url}, "role": "reference_image"})
+        if content_items is not None:
+            # 自由创作:调用方整段接管参考素材(混合 image/video/audio + role first_frame/last_frame 等)
+            content.extend(content_items)
+        else:
+            for image_url in reference_images or []:
+                content.append({"type": "image_url", "image_url": {"url": image_url}, "role": "reference_image"})
         body = {
             "model": model,
             "content": content,
@@ -208,6 +215,10 @@ class VolcanoArkProvider:
             # Seedance 直接出音效 + 人物声音(参考生视频);关掉则是哑片。默认开。
             "generate_audio": generate_audio,
         }
+        if seed is not None and seed != -1:
+            body["seed"] = seed
+        if search_mode == "smart":
+            body["tools"] = [{"type": "web_search"}]
         response = requests.post(
             f"{self.base_url.rstrip('/')}/{endpoint.lstrip('/')}",
             headers={"Authorization": f"Bearer {self.api_key}", "Content-Type": "application/json"},
@@ -236,9 +247,24 @@ class VolcanoArkProvider:
                 return item["url"]
             if item.get("b64_json"):
                 return item["b64_json"]
-        content = data.get("content") or {}
-        if content.get("video_url"):
-            return content["video_url"]
+        # 视频任务响应的 content 有两种形态:dict {video_url: "..."} 或
+        # list [{type:"video_url", video_url:{url:"..."}}](Seedance 2.0 多模态响应)。
+        content = data.get("content")
+        if isinstance(content, dict):
+            video_url = content.get("video_url")
+            if isinstance(video_url, str) and video_url:
+                return video_url
+            if isinstance(video_url, dict) and video_url.get("url"):
+                return video_url["url"]
+        if isinstance(content, list):
+            for item in content:
+                if not isinstance(item, dict):
+                    continue
+                video_url = item.get("video_url")
+                if isinstance(video_url, str) and video_url:
+                    return video_url
+                if isinstance(video_url, dict) and video_url.get("url"):
+                    return video_url["url"]
         raise ValueError("Volcano response does not contain media url")
 
     @staticmethod