refactor: 重构异步任务系统和计费服务架构

- 重构任务系统：新增 lifecycle (TaskStatus/BillingStatus)、context、application 模块
- 将 video tasks 泛化为 async tasks，支持更通用的异步任务管理
- 新增 Gemini Files 管理模块和管理界面
- 重构 billing 服务：拆分 schema.py 和 service.py
- 新增 candidate 服务模块用于请求候选管理
- 数据库迁移：添加 billing_status、request_id、gemini_file_mappings 表和索引
- 移除废弃的 video_telemetry、task orchestrator 等模块

src/services/orchestration/candidate_resolver.py

@@ -156,6 +156,8 @@ class CandidateResolver:
         user_id: str,
         user_api_key: ApiKey,
         required_capabilities: dict[str, bool] | None = None,
+        *,
+        expand_retries: bool = True,
     ) -> dict[tuple[int, int], str]:
         """
         为所有候选预先创建 available 状态记录（批量插入优化）
@@ -211,9 +213,12 @@ class CandidateResolver:
                 candidate_record_map[(candidate_index, 0)] = record_id
             else:
                 # max_retries 已从 Endpoint 迁移到 Provider（Endpoint 仍可能保留旧字段用于兼容）
-                max_retries_for_candidate = (
-                    int(provider.max_retries or 2) if candidate.is_cached else 1
-                )
+                if not expand_retries:
+                    max_retries_for_candidate = 1
+                else:
+                    max_retries_for_candidate = (
+                        int(provider.max_retries or 2) if candidate.is_cached else 1
+                    )
 
                 for retry_index in range(max_retries_for_candidate):
                     record_id = str(uuid.uuid4())