fix(members): correct installment panel formula and add live preview

- Installment panel in member show page now uses flat simple interest:
  remaining × (rate/100) × (months/12) instead of hardcoded 22% × 30mo
- Live breakdown table updates in real-time as user changes down payment
  or months: shows سعر العضوية, المقدم, المبلغ المتبقي, الفائدة,
  الإجمالي مع الفائدة, القسط الشهري
- Pass installInterestRate and installMaxMonths from RuleEngine to show view
- Fix pay-membership action to respect RuleEngine max months (not hardcoded 30)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Modules/Members/Controllers/MemberController.php

@@ -255,6 +255,9 @@ class MemberController extends Controller
             );
         }
 
+        $instRateData    = RuleEngine::get('INSTALLMENT_INTEREST_RATE');
+        $instMonthsData  = RuleEngine::get('INSTALLMENT_MAX_MONTHS');
+
         return $this->view('Members.Views.show', [
             'member' => $member,
             'branchName' => $branch['name_ar'] ?? '—',
@@ -276,6 +279,8 @@ class MemberController extends Controller
             'installmentPlan' => $member->status === 'pending_cheques'
                 ? $db->selectOne("SELECT id, number_of_months FROM installment_plans WHERE member_id = ? AND status = 'active' ORDER BY id DESC LIMIT 1", [(int) $id])
                 : null,
+            'installInterestRate' => (float) ($instRateData['percentage'] ?? 22),
+            'installMaxMonths'    => (int)   ($instMonthsData['months']   ?? 30),
         ]);
     }
 
@@ -367,7 +372,9 @@ class MemberController extends Controller
 
         if (bccomp($amount, '0.01', 2) < 0) return $this->redirect('/members/' . $id)->withError('المبلغ غير صالح');
 
-        $months = ($paymentType === 'down_payment') ? min(30, max(1, (int) $request->post('installment_months', 30))) : null;
+        $instMaxMonthsData = RuleEngine::get('INSTALLMENT_MAX_MONTHS');
+        $instMaxMonths = (int) ($instMaxMonthsData['months'] ?? 30);
+        $months = ($paymentType === 'down_payment') ? min($instMaxMonths, max(1, (int) $request->post('installment_months', $instMaxMonths))) : null;
 
         // Cancel any pending individual addition_fee requests — the collective payment subsumes them
         $pendingAdditions = $db->select(