feat(ExcelIO): add ExcelFormats constants

NEW/src/JdeScoping.ExcelIO/Mapping/ExcelFormats.cs

@@ -0,0 +1,19 @@
+namespace JdeScoping.ExcelIO.Mapping;
+
+/// <summary>
+/// Standard Excel format strings for column configuration.
+/// </summary>
+public static class ExcelFormats
+{
+    /// <summary>Text format (default).</summary>
+    public const string Text = "@";
+
+    /// <summary>Date format: MM/dd/yyyy</summary>
+    public const string Date = "[$-409]MM/dd/yyyy;@";
+
+    /// <summary>Timestamp format: m/d/yy h:mm AM/PM</summary>
+    public const string Timestamp = "[$-409]m/d/yy h:mm AM/PM;@";
+
+    /// <summary>Default width for wrapped text columns.</summary>
+    public const double WrappedColumnWidth = 65;
+}