Add project files.

BudgetApp/Data/Account.cs

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+using System.ComponentModel.DataAnnotations;
+
+namespace BudgetApp.Data;
+
+public class Account
+{
+    public int Id { get; set; }
+
+    [Required, MaxLength(100)]
+    public string Name { get; set; } = string.Empty;
+
+    public decimal CurrentBalance { get; set; }
+
+    [Required, MaxLength(7)]
+    public string Color { get; set; } = "#1b6ec2";
+
+    [Required, MaxLength(3)]
+    public string CurrencyCode { get; set; } = "GBP";
+
+    [Required]
+    public string UserId { get; set; } = string.Empty;
+
+    public ApplicationUser User { get; set; } = default!;
+
+    public List<Transaction> Transactions { get; set; } = [];
+
+    public static readonly Dictionary<string, string> CurrencySymbols = new()
+    {
+        ["USD"] = "$", ["EUR"] = "€", ["GBP"] = "£", ["JPY"] = "¥",
+        ["CAD"] = "C$", ["AUD"] = "A$", ["CHF"] = "CHF", ["CNY"] = "¥",
+        ["INR"] = "₹", ["BRL"] = "R$", ["KRW"] = "₩", ["MXN"] = "MX$",
+        ["SEK"] = "kr", ["NOK"] = "kr", ["DKK"] = "kr", ["NZD"] = "NZ$",
+        ["ZAR"] = "R", ["PLN"] = "zł", ["TRY"] = "₺", ["THB"] = "฿"
+    };
+
+    public string GetSymbol() => CurrencySymbols.GetValueOrDefault(CurrencyCode, CurrencyCode);
+
+    public string FormatAmount(decimal amount) => $"{GetSymbol()}{amount:N2}";
+}