feat: add TradeContext, Subcategory and LastAnalyzedAt

src/Predictalytics.Domain/Entities/Trade.cs

@@ -91,5 +91,9 @@ public class Trade
     // ── Navigation ────────────────────────────────────────────────────────
     public Trader Trader { get; set; } = null!;
     public MarketOutcome? MarketOutcome { get; set; }
+
+    /// <summary>Analytics context containing high-resolution price data and slippage (if collected).</summary>
+    public TradeContext? Context { get; set; }
+
     public Market? DbMarket { get; set; }
 }