feat: 日报事件多新闻源入库(news_event.sources 列)

- ExtractedEvent 增加 sources 字段(主源居首去重,旧产物兜底 [source_id])
- extract_event(_async) 增加 sources 参数;run_event_extraction 读取
  deduped uniques 的 sources 透传
- reporter _load_events_from_dir 读取 sources → EventRow.sources
- news_event 建表加 sources TEXT 列;init_schema 幂等迁移旧表(捕获
  Duplicate column);save_report INSERT 写 JSON 多源
- 新增测试:ExtractedEvent/EventRow.sources 兜底与保序、_load_events_from_dir 多源

report_db/models.py

@@ -18,7 +18,8 @@ class EventRow(BaseModel):
     title: str
     summary: str | None = None
     sentiment: str | None = None  # positive | negative | neutral | ''
-    source: str | None = None
+    source: str | None = None  # 主源
+    sources: list[str] | None = None  # 全部来源(主源居首),多源新闻记录
     url: str | None = None