Add NoOp email service, /docs shortcut and fix streak timezone bug

Replace nil email service pattern with NoOpEmailService (Null Object)
to eliminate nil pointer panics across all handlers.

Add /docs route as a shortcut to Swagger UI.

Fix streak calculation returning 0 when server timezone differs from
UTC — CreatedAt was not converted to UTC before date extraction.

internal/infrastructure/email/smtp_service.go

@@ -107,6 +107,10 @@ func (s *SMTPService) GetConfig() SMTPConfig {
 	return s.config
 }
 
+func (s *SMTPService) IsEnabled() bool {
+	return true
+}
+
 func (s *SMTPService) HealthCheck() error {
 	dialer := mail.NewDialer(s.config.Host, s.config.Port, s.config.Username, s.config.Password)
 	dialer.TLSConfig = &tls.Config{