feat(ExcelIO): add ColumnBuilder fluent API

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

@@ -0,0 +1,52 @@
+namespace JdeScoping.ExcelIO.Mapping;
+
+/// <summary>
+/// Fluent builder for configuring Excel column properties.
+/// </summary>
+/// <typeparam name="T">The model type being mapped.</typeparam>
+/// <typeparam name="TProperty">The property type.</typeparam>
+public sealed class ColumnBuilder<T, TProperty>
+{
+    private readonly ColumnDefinition _definition;
+
+    internal ColumnBuilder(ColumnDefinition definition)
+    {
+        _definition = definition;
+    }
+
+    /// <summary>Sets the column display order.</summary>
+    public ColumnBuilder<T, TProperty> Order(int order)
+    {
+        _definition.Order = order;
+        return this;
+    }
+
+    /// <summary>Sets the column header text.</summary>
+    public ColumnBuilder<T, TProperty> Header(string text)
+    {
+        _definition.HeaderText = text;
+        return this;
+    }
+
+    /// <summary>Sets the Excel number format.</summary>
+    public ColumnBuilder<T, TProperty> Format(string format)
+    {
+        _definition.Format = format;
+        return this;
+    }
+
+    /// <summary>Sets a fixed column width (disables auto-width).</summary>
+    public ColumnBuilder<T, TProperty> Width(double width)
+    {
+        _definition.AutoWidth = false;
+        _definition.Width = width;
+        return this;
+    }
+
+    /// <summary>Enables text wrapping for the column.</summary>
+    public ColumnBuilder<T, TProperty> WrapText(bool wrap = true)
+    {
+        _definition.WrapText = wrap;
+        return this;
+    }
+}