Fix API offset limit 400 Bad Request, implement requested UI/UX improvements

src/Predictalytics.Infrastructure/Data/Repositories/TraderRepository.cs

@@ -2,6 +2,7 @@ using Predictalytics.Domain.Entities;
 using Predictalytics.Domain.Enums;
 using Predictalytics.Domain.Interfaces;
 using Microsoft.EntityFrameworkCore;
+using System.Text;
 
 namespace Predictalytics.Infrastructure.Data.Repositories;
 
@@ -65,7 +66,29 @@ public class TraderRepository : ITraderRepository
     { _db.Traders.Add(trader); await _db.SaveChangesAsync(ct); }
 
     public async Task UpdateAsync(Trader trader, CancellationToken ct = default)
-    { _db.Traders.Update(trader); await _db.SaveChangesAsync(ct); }
+    {
+        _db.Traders.Update(trader);
+        await _db.SaveChangesAsync(ct);
+    }
+
+    public async Task UpdateRanksAsync(IEnumerable<(int TraderId, int Rank)> ranks, CancellationToken ct = default)
+    {
+        // Batch update ranks using raw SQL to avoid N+1 and loading entities
+        var sql = new StringBuilder();
+        sql.AppendLine("UPDATE TraderScores SET Rank = CASE TraderId");
+        var ids = new List<int>();
+        foreach (var r in ranks)
+        {
+            sql.AppendLine($"WHEN {r.TraderId} THEN {r.Rank}");
+            ids.Add(r.TraderId);
+        }
+        sql.AppendLine("ELSE Rank END WHERE TraderId IN (" + string.Join(",", ids) + ");");
+        
+        if (ids.Count > 0)
+        {
+            await _db.Database.ExecuteSqlRawAsync(sql.ToString(), ct);
+        }
+    }
 
     public async Task DeleteAsync(int id, CancellationToken ct = default)
     {