Add Jin10 QR connection with cancellable login tasks

Store account credentials encrypted and bind QR tasks to administrator sessions. Report calendar access as awaiting validation after login.

Prevent late polls and status responses from overwriting cancelled or newer operations, and clean up QR tasks when settings unmount. Cover authentication, cancellation races, and stale frontend responses.

backend/src/alphapulse/models/__init__.py

@@ -1,3 +1,4 @@
+from alphapulse.models.jin10 import Jin10Connection
 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
@@ -7,6 +8,7 @@ from alphapulse.models.news import CrawlLog, CrawlRun, NewsItem, NewsRevision, R
 from alphapulse.models.trading import NewsSignal, TradingAccount, TradingAnalysis, TradingCredential, TradingEvent, TradingFill, TradingOrder, TradingSymbol
 
 __all__ = [
+    "Jin10Connection",
     "RiskSettings", "RiskEvent", "RiskAnalysis", "RiskSnapshot",
     "AiProvider",
     "Base",