Support selectable demo exchanges and configurable analysis limits

Persist manual requests until exchange confirmation, preserve stop protection, and reconcile fills before settling plans. Tighten model stream, crawler, skill, research accounting, and frontend race handling, with regression coverage. Keep queued analyses pending until a fresh account snapshot is available.

backend/src/alphapulse/models/__init__.py

@@ -2,7 +2,7 @@ from alphapulse.core.db import Base
 from alphapulse.models.ai import AiProvider, ChatMessage, ChatSession, ContextVersion, SkillNode, SkillVersion
 from alphapulse.models.market import Kline, KlineSyncState, MarketSymbol
 from alphapulse.models.news import CrawlLog, CrawlRun, NewsItem, NewsRevision, RawBody, RawResponse, Source
-from alphapulse.models.trading import NewsSignal, TradingAccount, TradingAnalysis, TradingEvent, TradingFill, TradingOrder, TradingSymbol
+from alphapulse.models.trading import NewsSignal, TradingAccount, TradingAnalysis, TradingCredential, TradingEvent, TradingFill, TradingOrder, TradingSymbol
 
 __all__ = [
     "AiProvider",
@@ -25,6 +25,7 @@ __all__ = [
     "Source",
     "TradingAccount",
     "TradingAnalysis",
+    "TradingCredential",
     "TradingEvent",
     "TradingFill",
     "TradingOrder",