feat(1099): add Form1099BoxId mapping FKs and Expense.PayeeId

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

API/ROLAC.API/Entities/Expense.cs

@@ -11,6 +11,7 @@ public class Expense : SoftDeleteEntity, IAuditable
     public string   Description     { get; set; } = null!;
     public string?  VendorName      { get; set; }
     public int?     MemberId        { get; set; }
+    public int?      PayeeId { get; set; }   // 1099 recipient attribution (header-level)
     public string?  CheckNumber     { get; set; }
     public DateOnly ExpenseDate     { get; set; }
     public string?  ReceiptBlobPath { get; set; }
@@ -25,5 +26,6 @@ public class Expense : SoftDeleteEntity, IAuditable
 
     public Ministry?         Ministry { get; set; }
     public Member?           Member   { get; set; }
+    public Payee1099?        Payee    { get; set; }
     public List<ExpenseLine> Lines    { get; set; } = new();
 }

API/ROLAC.API/Entities/ExpenseCategoryGroup.cs

@@ -12,5 +12,8 @@ public class ExpenseCategoryGroup : AuditableEntity, IAuditable
     public int?                Form990LineId { get; set; }
     public Form990ExpenseLine? Form990Line   { get; set; }
 
+    public int?         Form1099BoxId { get; set; }   // null = not 1099-reportable
+    public Form1099Box? Form1099Box   { get; set; }
+
     public List<ExpenseSubCategory> SubCategories { get; set; } = [];
 }

API/ROLAC.API/Entities/ExpenseSubCategory.cs

@@ -13,5 +13,8 @@ public class ExpenseSubCategory : AuditableEntity, IAuditable
     public int?                Form990LineId { get; set; }
     public Form990ExpenseLine? Form990Line   { get; set; }
 
+    public int?         Form1099BoxId { get; set; }   // null = not 1099-reportable
+    public Form1099Box? Form1099Box   { get; set; }
+
     public ExpenseCategoryGroup? Group { get; set; }
 }