Three small UX fixes: customer contact validation, pagination dropdown width

- Customer validation now accepts Mobile Phone as a valid contact method;
  previously only Email or Phone satisfied the requirement
- Create customer hint text updated to match the new validation rule
- Pagination page-size dropdown gets min-width: 5rem so the number has
  breathing room from the caret arrow across all paginated lists

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Application/DTOs/Customer/CustomerDtos.cs

@@ -140,12 +140,12 @@ public class CreateCustomerDto : IValidatableObject
                 new[] { nameof(CompanyName), nameof(ContactFirstName), nameof(ContactLastName) });
         }
 
-        // At least one contact method is required (Email OR Phone)
+        // At least one contact method is required (Email, Phone, or Mobile Phone)
-        if (string.IsNullOrWhiteSpace(Email) && string.IsNullOrWhiteSpace(Phone))
+        if (string.IsNullOrWhiteSpace(Email) && string.IsNullOrWhiteSpace(Phone) && string.IsNullOrWhiteSpace(MobilePhone))
         {
             yield return new ValidationResult(
-                "Please provide at least one contact method (Email or Phone)",
+                "Please provide at least one contact method (Email, Phone, or Mobile Phone)",
-                new[] { nameof(Email), nameof(Phone) });
+                new[] { nameof(Email), nameof(Phone), nameof(MobilePhone) });
         }
 
         // Validate each address in comma-separated email fields

src/PowderCoating.Web/Views/Customers/Create.cshtml

@@ -59,7 +59,7 @@
                         </h5>
                         <div class="alert alert-info alert-permanent py-2 px-3 mb-3" style="font-size:.875rem;">
                             <i class="bi bi-info-circle me-1"></i>
-                            <strong>Required:</strong> At least one of Company Name, First Name, or Last Name — and at least one of Email or Phone.
+                            <strong>Required:</strong> At least one of Company Name, First Name, or Last Name — and at least one of Email, Phone, or Mobile Phone.
                         </div>
                         <div class="row g-3">
                             <div class="col-md-6">

src/PowderCoating.Web/Views/Shared/_Pagination.cshtml

@@ -24,7 +24,7 @@
                 <span class="me-2">Showing @Model.StartIndex-@Model.EndIndex of @Model.TotalCount results</span>
                 <span class="me-2">|</span>
                 <label class="me-2 mb-0">Page size:</label>
-                <select class="form-select form-select-sm w-auto" onchange="changePageSize(this.value)">
+                <select class="form-select form-select-sm w-auto" style="min-width: 5rem;" onchange="changePageSize(this.value)">
                     <option value="10" selected="@(Model.PageSize == 10)">10</option>
                     <option value="25" selected="@(Model.PageSize == 25)">25</option>
                     <option value="50" selected="@(Model.PageSize == 50)">50</option>