feat(news): index news packages and research persistent events

Extract reusable literal keywords once per source revision, assign complete news packages to long-lived events, and research all event members with immutable evidence and references.

Add additive research storage, vocabulary snapshots, the two-stage workspace, isolated acceptance coverage, and a paused rollout with an initial fixed 50-news production trial.

backend/tests/test_news_pipeline.py

@@ -12,7 +12,7 @@ def pipeline(trading):
 
 
 def match(pipeline, **changes):
-    return dict(package_id=None, group_key='event', title='公告', category='macro', entities=['央行'],
+    return dict(event=dict(event_id=None,group_key='event',title='公告',fact='公告',reason='同一具体事项'),package_id=None, group_key='event', title='公告', category='macro', entities=['央行'],
         fact='公告', evidence='公告', urgent=False, tags=['央行'], content_kind='report', **changes)