feat(expense): add Form990ExpenseLine catalog entity and functional-class constants

API/ROLAC.API/Entities/Form990ExpenseLine.cs

@@ -0,0 +1,13 @@
+using ROLAC.API.Entities.Base;
+namespace ROLAC.API.Entities;
+
+/// <summary>A row of IRS Form 990 Part IX (natural expense line), e.g. "7 — Other salaries and wages".</summary>
+public class Form990ExpenseLine : AuditableEntity, IAuditable
+{
+    public int     Id        { get; set; }
+    public string  LineCode  { get; set; } = null!;   // "7", "11b", "16", "24"
+    public string  Name_en   { get; set; } = null!;
+    public string? Name_zh   { get; set; }
+    public int     SortOrder { get; set; }
+    public bool    IsActive  { get; set; } = true;
+}

API/ROLAC.API/Entities/FunctionalClasses.cs

@@ -0,0 +1,18 @@
+namespace ROLAC.API.Entities;
+
+/// <summary>
+/// The three IRS Form 990 Part IX functional-expense columns. Stored verbatim in
+/// Ministry.DefaultFunctionalClass and Expense.FunctionalClass.
+/// </summary>
+public static class FunctionalClasses
+{
+    public const string Program           = "Program";
+    public const string ManagementGeneral = "ManagementGeneral";
+    public const string Fundraising       = "Fundraising";
+
+    public static readonly IReadOnlyList<string> All = [Program, ManagementGeneral, Fundraising];
+
+    /// <summary>Returns the value if valid, otherwise Program (the safe default).</summary>
+    public static string Normalize(string? value) =>
+        value is not null && All.Contains(value) ? value : Program;
+}