feat: implement Notion-like LMS (Course Player, Exam, Certificate) with R2 integration

app/Http/Controllers/CertificateController.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use App\Models\Course;
+use App\Models\UserProgress;
+use Illuminate\Http\Request;
+use Inertia\Inertia;
+use Barryvdh\DomPDF\Facade\Pdf; // Optional if we want PDF download, for now just view
+
+class CertificateController extends Controller
+{
+    public function show(Request $request, string $courseSlug)
+    {
+        $user = $request->user();
+        $course = Course::where('slug', $courseSlug)->withCount('lessons')->firstOrFail();
+
+        // Check if course is fully completed
+        // Count completed lessons vs total lessons
+        $completedCount = UserProgress::where('user_id', $user->id)
+            ->whereIn('lesson_id', $course->lessons()->pluck('id'))
+            ->whereNotNull('completed_at')
+            ->count();
+
+        $totalLessons = $course->lessons_count ?? 0;
+        $progress = ($totalLessons > 0) ? ($completedCount / $totalLessons) * 100 : 0;
+
+        // Strict check: Must be 100% complete
+        if ($progress < 100) {
+             return redirect()->route('courses.index')->with('error', 'Selesaikan semua materi untuk klaim sertifikat.');
+        }
+
+        return Inertia::render('Certificates/Show', [
+            'course' => $course,
+            'student' => $user,
+            'date' => now()->translatedFormat('d F Y'),
+            'certificate_id' => 'NB-' . strtoupper(substr($course->slug, 0, 3)) . '-' . $user->id . '-' . date('ymd'),
+        ]);
+    }
+}