Add Paper Trading Journal with analytics (#65)

- PaperTrade model extending ContextualEntry
- PaperTradeService with CRUD, close trade, and analytics
  - Summary stats (win rate, P&L)
  - Stats by pattern tag
  - Stats by gamma regime
  - Export as JSON/CSV
- PaperTrading.razor page with:
  - Open/Closed trade tabs
  - Analytics dashboard
  - New trade modal with direction, price, targets
  - Close trade modal with P&L preview
- Added to home page with green chart-line icon

Author: iAmGiG

src/GexVisor.UI/Models/PaperTrade.cs

@@ -0,0 +1,81 @@
+namespace GexVisor.UI.Models;
+
+/// <summary>
+/// Represents a hypothetical paper trade for tracking GEX-based trading strategies.
+/// </summary>
+public record PaperTrade : ContextualEntry
+{
+    /// <summary>Trade direction: "Long" or "Short".</summary>
+    public required string Direction { get; init; }
+
+    /// <summary>Entry price for the trade.</summary>
+    public required decimal EntryPrice { get; init; }
+
+    /// <summary>Optional target price for profit taking.</summary>
+    public decimal? TargetPrice { get; init; }
+
+    /// <summary>Optional stop loss price.</summary>
+    public decimal? StopLoss { get; init; }
+
+    /// <summary>Notes about the trade setup or reasoning.</summary>
+    public string? Notes { get; init; }
+
+    // Exit fields
+    /// <summary>Date when the trade was closed.</summary>
+    public DateTime? ExitDate { get; init; }
+
+    /// <summary>Exit price when the trade was closed.</summary>
+    public decimal? ExitPrice { get; init; }
+
+    /// <summary>Reason for exit: "Target", "Stop", "Manual", "Time".</summary>
+    public string? ExitReason { get; init; }
+
+    // Computed properties
+    /// <summary>Whether the trade is still open.</summary>
+    public bool IsOpen => ExitDate == null;
+
+    /// <summary>P&L in price points (null if trade is open).</summary>
+    public decimal? PnLPoints => ExitPrice.HasValue
+        ? (ExitPrice.Value - EntryPrice) * (Direction == "Long" ? 1 : -1)
+        : null;
+
+    /// <summary>P&L as a percentage (null if trade is open).</summary>
+    public decimal? PnLPercent => PnLPoints.HasValue && EntryPrice != 0
+        ? PnLPoints.Value / EntryPrice * 100
+        : null;
+
+    /// <summary>Whether the trade was profitable.</summary>
+    public bool? IsWin => PnLPoints.HasValue ? PnLPoints.Value > 0 : null;
+
+    /// <summary>Current unrealized P&L based on a given current price.</summary>
+    public decimal GetUnrealizedPnL(decimal currentPrice)
+    {
+        return (currentPrice - EntryPrice) * (Direction == "Long" ? 1 : -1);
+    }
+
+    /// <summary>Current unrealized P&L percentage based on a given current price.</summary>
+    public decimal GetUnrealizedPnLPercent(decimal currentPrice)
+    {
+        return EntryPrice != 0 ? GetUnrealizedPnL(currentPrice) / EntryPrice * 100 : 0;
+    }
+}
+
+/// <summary>
+/// Direction constants for paper trades.
+/// </summary>
+public static class TradeDirection
+{
+    public const string Long = "Long";
+    public const string Short = "Short";
+}
+
+/// <summary>
+/// Exit reason constants for paper trades.
+/// </summary>
+public static class ExitReason
+{
+    public const string Target = "Target";
+    public const string Stop = "Stop";
+    public const string Manual = "Manual";
+    public const string Time = "Time";
+}

src/GexVisor.UI/Pages/Index.razor

@@ -47,6 +47,19 @@
                 </div>
             </div>
         </a>
+
+        <a href="/trading" class="app-card">
+            <div class="app-icon trading">
+                <i class="fas fa-chart-line"></i>
+            </div>
+            <div class="app-info">
+                <h2>Paper Trading</h2>
+                <p>Log hypothetical trades based on GEX signals and track theoretical P&L</p>
+                <div class="app-status ready">
+                    <i class="fas fa-check-circle"></i> Ready
+                </div>
+            </div>
+        </a>
     </div>
 
     <footer class="landing-footer">

src/GexVisor.UI/Pages/Index.razor.css

@@ -94,6 +94,11 @@
     color: white;
 }
 
+.app-icon.trading {
+    background: linear-gradient(135deg, var(--accent-green), #1b5e20);
+    color: white;
+}
+
 .app-info {
     flex: 1;
 }