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/src/alphapulse/api/main.py

@@ -5,7 +5,8 @@ from fastapi.exceptions import RequestValidationError
 from fastapi.responses import RedirectResponse
 from starlette.exceptions import HTTPException
 
-from alphapulse.api import auth, calendar, chat, crawler, market, news, settings, skills, trading, risk, jin10
+from alphapulse.api import auth, calendar, chat, crawler, market, news, settings, skills, trading, jin10
+from alphapulse.news_research import api as risk
 from alphapulse.api.response import (
     ApiResponse, ValidationErrors, http_error, internal_error, success, validation_error,
 )