feat: Docker Compose setup untuk development & production

- docker/php/Dockerfile: PHP 8.4-FPM + GD + imagick (PECL) + semua extension Laravel
- docker/php/php.ini: upload 20MB, memory 512MB, opcache, Asia/Kuala_Lumpur
- docker/php/php-dev.ini: validate_timestamps=1, display_errors=On (dev)
- docker/nginx/default.conf: gzip, security headers, static asset caching
- docker/entrypoint.sh: tunggu MySQL → migrate → seed AdminSeeder → cache (prod)
- docker-compose.yml: dev stack — port 8003, DB host 33060, queue worker
- docker-compose.prod.yml: production overrides — storage volume, no DB port exposed
- .env.docker: template env untuk Docker (DB_HOST=db)
- .dockerignore: exclude node_modules, vendor, .env, logs

fix: testGenerate try/catch kembalikan JSON error (bukan HTML 500)
fix: loadPreview() semak r.ok, tunjuk error alert, loading spinner

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

resources/views/admin/programs/template/show.blade.php

@@ -54,7 +54,7 @@
                                    value="NAMA PESERTA CONTOH" placeholder="Nama untuk pratonton">
                         </div>
                         <div class="col-4">
-                            <button type="button" class="btn btn-sm btn-primary w-100" onclick="loadPreview()">
+                            <button type="button" id="previewBtn" class="btn btn-sm btn-primary w-100" onclick="loadPreview()">
                                 <i class="bi bi-eye me-1"></i> Pratonton
                             </button>
                         </div>
@@ -247,18 +247,34 @@ function toggleCertNo(cb) {
 }
 
 function loadPreview() {
-    const name = document.getElementById('sampleName').value || 'NAMA PESERTA CONTOH';
+    const name = document.getElementById('sampleName').value.trim() || 'NAMA PESERTA CONTOH';
     const img  = document.getElementById('templatePreview');
+    const btn  = document.getElementById('previewBtn');
     const url  = "{{ route('admin.programs.template.test', $program) }}";
 
+    btn.disabled = true;
+    btn.innerHTML = '<span class="spinner-border spinner-border-sm me-1" role="status"></span> Memuatkan...';
+
     const form = new FormData();
     form.append('_token', '{{ csrf_token() }}');
     form.append('sample_name', name);
 
     fetch(url, { method: 'POST', body: form })
-        .then(r => r.blob())
+        .then(r => {
+            if (!r.ok) return r.json().then(j => { throw new Error(j.error || 'Ralat pelayan (' + r.status + ')'); });
+            return r.blob();
+        })
         .then(blob => {
+            const prevSrc = img.src;
             img.src = URL.createObjectURL(blob);
+            if (prevSrc.startsWith('blob:')) URL.revokeObjectURL(prevSrc);
+        })
+        .catch(err => {
+            alert('Gagal jana pratonton: ' + err.message);
+        })
+        .finally(() => {
+            btn.disabled = false;
+            btn.innerHTML = '<i class="bi bi-eye me-1"></i> Pratonton';
         });
 }
 </script>