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)

.env.example

@@ -10,3 +10,18 @@ REFRESH_TOKEN_EXPIRY=7d
 CORS_ORIGINS=http://localhost:3000
 
 DEFAULT_TIMEZONE=UTC
+
+# Email Configuration (optional - required for email features)
+SMTP_HOST=
+SMTP_PORT=587
+SMTP_USER=
+SMTP_PASSWORD=
+
+# Application Branding (optional - override support email if needed)
+SUPPORT_EMAIL=contact@apocapoc.app
+
+# Email Features
+SEND_WELCOME_EMAIL=false
+
+# Registration Control
+REGISTRATION_MODE=open