fix: pratonton guna koordinat form semasa, No. Sijil ikut toggle

- loadPreview() hantar semua nilai field (X, Y, font_size, color, align) ke endpoint
- certificate_no disertakan hanya jika toggle showCertNo aktif
- testGenerate() bina liveFields dari request, gabung dengan config tersimpan
  (supaya font_file & valign kekal dari config asal)
- generatePreview() terima overrideFields optional — preview sentiasa refresh

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

app/Http/Controllers/Admin/CertificateTemplateController.php

@@ -102,8 +102,19 @@ class CertificateTemplateController extends Controller
         $sampleName = $request->input('sample_name', 'NAMA PESERTA CONTOH');
         $sampleNo   = $request->input('sample_no', 'ECT/2025/0001');
 
+        // Bina override dari nilai form semasa (belum disimpan)
+        // Gabung dengan config tersimpan supaya font_file & valign kekal
+        $liveFields = null;
+        if ($request->has('fields') && is_array($request->input('fields'))) {
+            $saved      = $template->config_json['fields'] ?? [];
+            $liveFields = [];
+            foreach ($request->input('fields') as $key => $cfg) {
+                $liveFields[$key] = array_merge($saved[$key] ?? [], array_filter($cfg, fn($v) => $v !== null && $v !== ''));
+            }
+        }
+
         try {
-            $imageData = $service->generatePreview($template, $sampleName, $sampleNo);
+            $imageData = $service->generatePreview($template, $sampleName, $sampleNo, $liveFields);
         } catch (\Throwable $e) {
             return response()->json(['error' => $e->getMessage()], 500);
         }