fix(members): prevent empty string for decimal addition_fee in retroactive wizard

Empty form fields post as '' which ?? doesn't catch (only null). MySQL
rejects '' for decimal columns. Switched to ?: so empty strings fall
through to the '0.00' default.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Modules/Members/Controllers/RetroactiveWizardController.php

@@ -200,7 +200,7 @@ class RetroactiveWizardController extends Controller
                     'marriage_date'   => $post["spouse_marriage_date_{$i}"] ?? null,
                     'phone_mobile'    => $post["spouse_phone_{$i}"] ?? null,
                     'join_date'       => $post["spouse_join_date_{$i}"] ?? ($post['join_date'] ?? date('Y-m-d')),
-                    'addition_fee'    => $post["spouse_fee_{$i}"] ?? '0.00',
+                    'addition_fee'    => $post["spouse_fee_{$i}"] ?: '0.00',
                     'has_separate_fee'=> !empty($post["spouse_separate_fee_{$i}"]),
                     'payment_method'  => $post["spouse_pay_method_{$i}"] ?? 'cash',
                     'payment_date'    => $post["spouse_pay_date_{$i}"] ?? null,
@@ -218,7 +218,7 @@ class RetroactiveWizardController extends Controller
                     'date_of_birth'   => $post["child_dob_{$i}"] ?? null,
                     'gender'          => $post["child_gender_{$i}"] ?? 'male',
                     'join_date'       => $post["child_join_date_{$i}"] ?? ($post['join_date'] ?? date('Y-m-d')),
-                    'addition_fee'    => $post["child_fee_{$i}"] ?? '0.00',
+                    'addition_fee'    => $post["child_fee_{$i}"] ?: '0.00',
                     'has_separate_fee'=> !empty($post["child_separate_fee_{$i}"]),
                     'payment_method'  => $post["child_pay_method_{$i}"] ?? 'cash',
                     'payment_date'    => $post["child_pay_date_{$i}"] ?? null,
@@ -238,7 +238,7 @@ class RetroactiveWizardController extends Controller
                     'category'               => $post["temp_category_{$i}"] ?? 'parent',
                     'relationship_to_member' => $post["temp_relationship_{$i}"] ?? null,
                     'join_date'              => $post["temp_join_date_{$i}"] ?? ($post['join_date'] ?? date('Y-m-d')),
-                    'addition_fee'           => $post["temp_fee_{$i}"] ?? '0.00',
+                    'addition_fee'           => $post["temp_fee_{$i}"] ?: '0.00',
                     'has_separate_fee'       => !empty($post["temp_separate_fee_{$i}"]),
                     'payment_method'         => $post["temp_pay_method_{$i}"] ?? 'cash',
                     'payment_date'           => $post["temp_pay_date_{$i}"] ?? null,

app/Modules/Members/Services/RetroactiveMembershipService.php

@@ -240,7 +240,7 @@ final class RetroactiveMembershipService
                         'marriage_date'   => self::safeDate($spouse['marriage_date'] ?? null) ?? $joinDate,
                         'join_date'       => $spouseJoinDate,
                         'classification'  => 'working',
-                        'addition_fee'    => $spouse['addition_fee'] ?? '0.00',
+                        'addition_fee'    => $spouse['addition_fee'] ?: '0.00',
                         'status'          => 'active',
                         'activated_by_payment_id' => $membershipPaymentId,
                         'is_archived'     => 0,
@@ -292,7 +292,7 @@ final class RetroactiveMembershipService
                         'gender'          => $childGender ?: 'male',
                         'relationship'    => $childGender === 'female' ? 'daughter' : 'son',
                         'classification'  => 'included',
-                        'addition_fee'    => $child['addition_fee'] ?? '0.00',
+                        'addition_fee'    => $child['addition_fee'] ?: '0.00',
                         'status'          => 'active',
                         'activated_by_payment_id' => $membershipPaymentId,
                         'join_date'       => $childJoinDate,
@@ -344,7 +344,7 @@ final class RetroactiveMembershipService
                         'relationship_to_member' => self::emptyToNull($temp['relationship_to_member'] ?? null),
                         'status'                 => 'active',
                         'join_date'              => $tempJoinDate,
-                        'addition_fee'           => $temp['addition_fee'] ?? '0.00',
+                        'addition_fee'           => $temp['addition_fee'] ?: '0.00',
                         'is_archived'            => 0,
                         'created_at'             => self::safeTimestamp($tempJoinDate),
                         'updated_at'             => $ts,