feat(1099): add payer EIN to ChurchProfile (entity, DTO, migration)

Add PayerEin (nullable string, max 20) to ChurchProfile entity, AppDbContext
config, ChurchProfileDto response, UpdateChurchProfileRequest, and
ChurchProfileService round-trip — mirroring the Phone/BankRoutingNumber
nullable-string pattern. Migration AddPayerEinToChurchProfile adds only the
one nullable column to ChurchProfiles.

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

API/ROLAC.API/DTOs/Disbursement/ChurchProfileDtos.cs

@@ -16,6 +16,7 @@ public class ChurchProfileDto
     public string? BankName          { get; set; }
     public string? BankAccountNumber { get; set; }
     public string? BankRoutingNumber { get; set; }
+    public string? PayerEin          { get; set; }
     public int     NextCheckNumber   { get; set; }
     public string  AiProvider         { get; set; } = "Claude";
     public string? ClaudeModel        { get; set; }
@@ -38,6 +39,7 @@ public class UpdateChurchProfileRequest
     [MaxLength(200)] public string? BankName { get; set; }
     [MaxLength(50)]  public string? BankAccountNumber { get; set; }
     [MaxLength(50)]  public string? BankRoutingNumber { get; set; }
+    [MaxLength(20)]  public string? PayerEin          { get; set; }
     [Range(1, int.MaxValue)] public int NextCheckNumber { get; set; }
     [MaxLength(20)]  public string  AiProvider   { get; set; } = "Claude";
     [MaxLength(100)] public string? ClaudeModel  { get; set; }