Support internationalized domain names (IDN) in email validation

Add IdnEmail validation rule that converts IDN domains to Punycode
via idn_to_ascii() before validating with FILTER_VALIDATE_EMAIL.
Applied to all email fields: customers, members, profiles, admin
users, customer portal profiles, and mail configuration.

Includes unit tests for standard emails, IDN emails, and invalid
inputs.

Fixes #388

app/Http/Requests/CustomerRequest.php

@@ -3,6 +3,7 @@
 namespace App\Http\Requests;
 
 use App\Models\Address;
+use App\Rules\IdnEmail;
 use Illuminate\Foundation\Http\FormRequest;
 use Illuminate\Support\Arr;
 use Illuminate\Validation\Rule;
@@ -27,7 +28,7 @@ class CustomerRequest extends FormRequest
                 'required',
             ],
             'email' => [
-                'email',
+                new IdnEmail,
                 'nullable',
                 Rule::unique('customers')->where('company_id', $this->header('company')),
             ],
@@ -116,7 +117,7 @@ class CustomerRequest extends FormRequest
 
         if ($this->isMethod('PUT') && $this->email != null) {
             $rules['email'] = [
-                'email',
+                new IdnEmail,
                 'nullable',
                 Rule::unique('customers')->where('company_id', $this->header('company'))->ignore($this->route('customer')->id),
             ];