Add authenticated global economic calendar with Jin10 fallback

Collect macroeconomic releases, events and holidays through the official browser SDK with resumable history from 2025. Preserve evidence, revisions and observation times, and merge verified series with official fields taking priority.

Add category filters, field provenance, coverage and connection status. Verify calendar persistence and deployment recovery in isolated acceptance checks.

backend/src/alphapulse/models/__init__.py

@@ -1,4 +1,4 @@
-from alphapulse.models.jin10 import Jin10Connection
+from alphapulse.models.jin10 import Jin10Connection, Jin10SyncDay
 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
@@ -9,6 +9,7 @@ from alphapulse.models.trading import NewsSignal, TradingAccount, TradingAnalysi
 
 __all__ = [
     "Jin10Connection",
+    "Jin10SyncDay",
     "RiskSettings", "RiskEvent", "RiskAnalysis", "RiskSnapshot",
     "AiProvider",
     "Base",