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.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">