feat: email blast for certificates (Fasa 8)

- CertificateReadyMail: Mailable with Malay HTML email template
- SendCertificateEmailJob: dispatch per-certificate email, log to email_logs
- Email template: HTML with download link, program details, branding

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

app/Mail/CertificateReadyMail.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Mail;
+
+use App\Models\Certificate;
+use Illuminate\Bus\Queueable;
+use Illuminate\Mail\Mailable;
+use Illuminate\Mail\Mailables\Content;
+use Illuminate\Mail\Mailables\Envelope;
+use Illuminate\Queue\SerializesModels;
+
+class CertificateReadyMail extends Mailable
+{
+    use Queueable, SerializesModels;
+
+    public function __construct(public readonly Certificate $certificate) {}
+
+    public function envelope(): Envelope
+    {
+        return new Envelope(
+            subject: 'Sijil Digital Program — ' . $this->certificate->program->title,
+        );
+    }
+
+    public function content(): Content
+    {
+        return new Content(
+            view: 'emails.certificate-ready',
+        );
+    }
+}