feat: complete email infrastructure with queue, templates, logging, and API

Adds the full transactional email system:
- Redis queue (QUEUE_CONNECTION=redis), SES config in .env.example
- 3 migrations: organisation_email_settings, organisation_email_templates, email_logs
- EmailTemplateType and EmailLogStatus enums with Dutch defaults
- EmailService as central entry point for all email sending
- SendTransactionalEmail queued job with retries and idempotency
- TransactionalMail mailable with responsive HTML + plain text templates
- Organisation-level branding (colors, logo, footer, reply-to)
- Per-type template overrides with {variable} substitution
- Email log with filtering by status, type, date range, recipient
- Preview and send-test endpoints for template management
- API endpoints: email-settings, email-templates (CRUD), email-logs (read-only)
- Integrated into existing flows: invitations, password reset, email
  verification, registration approval/rejection
- 37 new tests across 4 test files, all existing tests updated

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/Models/Organisation.php

@@ -9,6 +9,7 @@ use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsToMany;
 use Illuminate\Database\Eloquent\Relations\HasMany;
+use Illuminate\Database\Eloquent\Relations\HasOne;
 use Illuminate\Database\Eloquent\SoftDeletes;
 
 final class Organisation extends Model
@@ -72,4 +73,19 @@ final class Organisation extends Model
     {
         return $this->hasMany(RegistrationFieldTemplate::class);
     }
+
+    public function emailSettings(): HasOne
+    {
+        return $this->hasOne(OrganisationEmailSettings::class);
+    }
+
+    public function emailTemplates(): HasMany
+    {
+        return $this->hasMany(OrganisationEmailTemplate::class);
+    }
+
+    public function emailLogs(): HasMany
+    {
+        return $this->hasMany(EmailLog::class);
+    }
 }