Add AI news risk analysis and dashboard

Analyze news revisions with independent model settings, evidence-backed risk ratings, event grouping, and rolling market outlooks. Add a default homepage, archival history, pending-result refresh, and isolated regression coverage.

Keep analysis disabled until explicitly enabled. Require a separately authorized schema migration before deployment and preserve compatibility with the previous six-service instance.

backend/src/alphapulse/models/__init__.py

@@ -1,3 +1,4 @@
+from alphapulse.models.risk import RiskSettings, RiskEvent, RiskAnalysis, RiskSnapshot
 from alphapulse.core.db import Base
 from alphapulse.models.ai import AiProvider, ChatMessage, ChatSession, ContextVersion, SkillNode, SkillVersion
 from alphapulse.models.calendar import EconomicRelease, EconomicRevision, EconomicSeriesValue
@@ -6,6 +7,7 @@ from alphapulse.models.news import CrawlLog, CrawlRun, NewsItem, NewsRevision, R
 from alphapulse.models.trading import NewsSignal, TradingAccount, TradingAnalysis, TradingCredential, TradingEvent, TradingFill, TradingOrder, TradingSymbol
 
 __all__ = [
+    "RiskSettings", "RiskEvent", "RiskAnalysis", "RiskSnapshot",
     "AiProvider",
     "Base",
     "ChatMessage",