refactor(repository): extract AsyncJobRepository base class for analysis/comparison

提取 AsyncJobRepository 泛型基类，消除 CampaignAnalysisRepository 和
CampaignPeriodComparisonRepository 的重复代码。基类提供 get_by_campaign
和 mark_orphans_failed 通用逻辑，子类只需指定 _table 类型和实现 upsert。

- 新增 AsyncJobRepository[DB] 泛型基类
- mark_orphans_failed 接受 error_message 参数，子类传入特定错误信息
- 删除约 60 行重复代码（两个 __init__、两个 get_by_campaign、两个 mark_orphans_failed 实现）
- 所有测试通过，行为不变

backend/agenteval/storage/repository.py

@@ -445,16 +445,46 @@ class CampaignRepository(BaseRepository[Campaign, CampaignDB]):
         self.session.refresh(db)
 
 
-class CampaignAnalysisRepository:
-    """Repository for campaign analysis rows (one per campaign, upserted)."""
+class AsyncJobRepository(Generic[DB]):
+    """Base class for async job repositories (analysis, comparison).
+
+    Provides common pattern: get_by_campaign, mark_orphans_failed.
+    Subclasses implement upsert with their specific fields.
+    """
+
+    _table: type[DB]
 
     def __init__(self, session: Optional[Session] = None):
         self.session = session or get_session()
 
-    def get_by_campaign(self, campaign_id: str) -> Optional[CampaignAnalysisDB]:
-        statement = select(CampaignAnalysisDB).where(CampaignAnalysisDB.campaign_id == campaign_id)
+    def get_by_campaign(self, campaign_id: str) -> Optional[DB]:
+        statement = select(self._table).where(self._table.campaign_id == campaign_id)  # type: ignore[attr-defined]
         return self.session.exec(statement).first()
 
+    def mark_orphans_failed(self, error_message: str) -> int:
+        """服务启动时清理：把滞留的 generating 行标记为 failed。
+
+        异步任务是进程内 asyncio 任务，服务重启后不会恢复；不清理则这些
+        行永远停留在 generating（僵尸状态）。
+        """
+        rows = self.session.exec(
+            select(self._table).where(self._table.status == "generating")  # type: ignore[attr-defined]
+        ).all()
+        for row in rows:
+            row.status = "failed"  # type: ignore[attr-defined]
+            row.error = error_message  # type: ignore[attr-defined]
+            row.updated_at = utc_now()  # type: ignore[attr-defined]
+            self.session.add(row)
+        if rows:
+            self.session.commit()
+        return len(rows)
+
+
+class CampaignAnalysisRepository(AsyncJobRepository[CampaignAnalysisDB]):
+    """Repository for campaign analysis rows (one per campaign, upserted)."""
+
+    _table = CampaignAnalysisDB
+
     def upsert(
         self,
         campaign_id: str,
@@ -483,31 +513,14 @@ class CampaignAnalysisRepository:
         return row
 
     def mark_orphans_failed(self) -> int:
-        """服务启动时清理：把滞留的 generating 分析行标记为 failed。
-
-        分析任务是进程内 asyncio 任务，服务重启后不会恢复；不清理则这些
-        行永远停留在 generating（僵尸状态）。
-        """
-        rows = self.session.exec(select(CampaignAnalysisDB).where(CampaignAnalysisDB.status == "generating")).all()
-        for row in rows:
-            row.status = "failed"
-            row.error = "服务重启导致分析生成中断"
-            row.updated_at = utc_now()
-            self.session.add(row)
-        if rows:
-            self.session.commit()
-        return len(rows)
+        """服务启动时清理：把滞留的 generating 分析行标记为 failed。"""
+        return super().mark_orphans_failed("服务重启导致分析生成中断")
 
 
-class CampaignPeriodComparisonRepository:
+class CampaignPeriodComparisonRepository(AsyncJobRepository[CampaignPeriodComparisonDB]):
     """Repository for period-comparison rows (one per campaign, upserted)."""
 
-    def __init__(self, session: Optional[Session] = None):
-        self.session = session or get_session()
-
-    def get_by_campaign(self, campaign_id: str) -> Optional[CampaignPeriodComparisonDB]:
-        statement = select(CampaignPeriodComparisonDB).where(CampaignPeriodComparisonDB.campaign_id == campaign_id)
-        return self.session.exec(statement).first()
+    _table = CampaignPeriodComparisonDB
 
     def upsert(
         self,
@@ -543,22 +556,8 @@ class CampaignPeriodComparisonRepository:
         return row
 
     def mark_orphans_failed(self) -> int:
-        """服务启动时清理：把滞留的 generating 周期对比行标记为 failed。
-
-        对比任务是进程内 asyncio 任务，服务重启后不会恢复；不清理则这些
-        行永远停留在 generating（僵尸状态）。基线配对保留，可直接重新触发。
-        """
-        rows = self.session.exec(
-            select(CampaignPeriodComparisonDB).where(CampaignPeriodComparisonDB.status == "generating")
-        ).all()
-        for row in rows:
-            row.status = "failed"
-            row.error = "服务重启导致周期对比生成中断"
-            row.updated_at = utc_now()
-            self.session.add(row)
-        if rows:
-            self.session.commit()
-        return len(rows)
+        """服务启动时清理：把滞留的 generating 周期对比行标记为 failed。"""
+        return super().mark_orphans_failed("服务重启导致周期对比生成中断")
 
 
 class ResultRepository: