Add demo trading page, trader snapshot service and trading tables

Add trading_symbols, trading_analyses, trading_orders and trading_events.
The new trader service publishes account, position and open-order
snapshots of the Binance demo account to Redis every 3s. The /trading
page shows engine status, start/stop, balances, positions, the symbol
list with angle selection, open orders and the event timeline.

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 TradingAccount
+from alphapulse.models.trading import TradingAccount, TradingAnalysis, TradingEvent, TradingOrder, TradingSymbol
 
 __all__ = [
     "AiProvider",
@@ -23,4 +23,8 @@ __all__ = [
     "SkillVersion",
     "Source",
     "TradingAccount",
+    "TradingAnalysis",
+    "TradingEvent",
+    "TradingOrder",
+    "TradingSymbol",
 ]