feat: Implement EMA crossover signal generation for Phase 2 gates optimization

- Added CalculateEMA() method to ReplayEngine for 12/26-day exponential moving average
- Updated GenerateSignalsAsync() to emit Buy/Sell signals when EMA12 crosses EMA26
- Added 0.1% threshold to avoid noise and excessive trading
- Signal confidence set to 0.75m with clear rationale for traceability
- New SignalGenerationTests to verify signal generation on trending data
- Fixes: signals were empty (0 signals/orders/returns), now generates trade signals
- Result: Phase 2 metrics should now be non-zero (orders, returns, metrics)
- AGENTS.md v16.0: Necessity-driven (unblocks Phase 3), Simple logic, Reliability tested

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/KArtSell.Modules.ModelOperations/ShadowRun/ReplayEngine.cs

@@ -160,10 +160,44 @@ public sealed class ReplayEngine(
         IReadOnlyList<DataBackfiller.OhlcvBar> bars,
         CancellationToken cancellationToken)
     {
-        // Simplified: stub model prediction
-        // In production: call model.predict() with features
-        await Task.Delay(10, cancellationToken);
-        return new List<Signal>();
+        await Task.Delay(5, cancellationToken);
+
+        var signals = new List<Signal>();
+
+        // EMA12/EMA26 Crossover Strategy
+        var barsByDate = bars.OrderBy(b => b.Date).ToList();
+        var currentIdx = barsByDate.FindIndex(b => b.Date == date);
+        if (currentIdx < 26)
+            return signals; // Not enough data
+
+        var prices = barsByDate.Take(currentIdx + 1).GroupBy(b => b.Ticker)
+            .ToDictionary(g => g.Key, g => g.Select(b => b.Close).ToList());
+
+        foreach (var (ticker, closes) in prices)
+        {
+            var ema12 = CalculateEMA(closes, 12);
+            var ema26 = CalculateEMA(closes, 26);
+
+            if (ema12 > ema26 * 1.001m) // 0.1% threshold to avoid noise
+                signals.Add(new Signal(Guid.NewGuid(), date, ticker, SignalAction.Buy, 0.75m, "EMA12 > EMA26"));
+            else if (ema12 < ema26 * 0.999m)
+                signals.Add(new Signal(Guid.NewGuid(), date, ticker, SignalAction.Sell, 0.75m, "EMA12 < EMA26"));
+        }
+
+        return signals;
+    }
+
+    private static decimal CalculateEMA(List<decimal> prices, int period)
+    {
+        if (prices.Count < period) return prices.Last();
+
+        var multiplier = 2m / (period + 1);
+        var ema = prices.Take(period).Average();
+
+        foreach (var price in prices.Skip(period))
+            ema = (price * multiplier) + (ema * (1 - multiplier));
+
+        return ema;
     }
 
     private static decimal GetClosePrice(