feat: Implement copytrading analytics and update WebUI

- Add v4 Tape-based CopytradingEstimator (Clustering, MAE, Tape Fills)
- Add CopytradingBacktestHarness (Walk-Forward testing, Shrinkage, LCB ranking)
- Add EF Core Migrations for FollowerFillPrice and Scoring fields
- Update WebUI: Fix Trader Detail tab layout blowout
- Update WebUI: Redesign Trader Detail menubar
- Update WebUI: Display separate Quality and Copyability metric cards
- Update WebUI: Add 'Highly Copyable' filter to Trader List

src/Predictalytics.Domain/Entities/TradeContext.cs

@@ -21,6 +21,12 @@ public class TradeContext
     /// <summary>The estimated mid-price of the asset roughly 1 minute after the trade execution.</summary>
     public decimal? PriceAfter1m { get; set; }
 
+    /// <summary>The volume-weighted exact follower fill price 10 seconds after the trade execution (excluding the trader's own trades).</summary>
+    public decimal? FollowerFillPrice10s { get; set; }
+
+    /// <summary>The volume-weighted exact follower fill price 60 seconds after the trade execution (excluding the trader's own trades).</summary>
+    public decimal? FollowerFillPrice60s { get; set; }
+
     /// <summary>Calculated slippage: execution price vs PriceBefore1m.</summary>
     public decimal? EstimatedSlippage { get; set; }