Add optional email verification and registration control

Implemented email service infrastructure with SMTP support and optional email verification for self-hosted deployments. Registration flow now supports open/closed modes and hardcoded Apocapoc branding.

Key features:
- Email service with SMTP and template rendering
- Optional email verification (auto-verified without SMTP config)
- Registration modes: open/closed for access control
- Hardcoded Apocapoc branding (AppName, AppURL, DefaultFrom)
- Separate registration and login flows (registration no longer returns tokens)

internal/infrastructure/email/smtp_service_test.go

@@ -0,0 +1,64 @@
+package email
+
+import (
+	"testing"
+
+	"apocapoc-api/internal/domain/services"
+)
+
+func TestNewSMTPService(t *testing.T) {
+	config := SMTPConfig{
+		Host:         "smtp.example.com",
+		Port:         587,
+		Username:     "user@example.com",
+		Password:     "password",
+		From:         "noreply@example.com",
+		SupportEmail: "support@example.com",
+	}
+
+	service := NewSMTPService(config)
+
+	if service == nil {
+		t.Fatal("Expected service to be created")
+	}
+
+	if service.GetConfig().Host != config.Host {
+		t.Errorf("Expected host %s, got %s", config.Host, service.GetConfig().Host)
+	}
+}
+
+func TestSMTPService_MessageConstruction(t *testing.T) {
+	config := SMTPConfig{
+		Host:         "smtp.example.com",
+		Port:         587,
+		Username:     "user@example.com",
+		Password:     "password",
+		From:         "noreply@example.com",
+		SupportEmail: "support@example.com",
+	}
+
+	service := NewSMTPService(config)
+
+	message := services.EmailMessage{
+		To:      "recipient@example.com",
+		Subject: "Test Email",
+		Body:    "<h1>Test</h1>",
+		IsHTML:  true,
+	}
+
+	if message.To == "" {
+		t.Error("Expected recipient to be set")
+	}
+
+	if message.Subject == "" {
+		t.Error("Expected subject to be set")
+	}
+
+	if !message.IsHTML {
+		t.Error("Expected message to be HTML")
+	}
+
+	if service == nil {
+		t.Fatal("Service should not be nil")
+	}
+}