Remove Gateway service and configuration

- Delete Gateway module, associated Spring Boot application, and related configuration (`GatewayApplication.java`, `application.yml`, and `pom.xml`).
- Remove Gateway references in `docker-compose.yml`, `.gitlab-ci.yml`, and `backend/pom.xml`.
- Update backend services to directly handle requests under `/api` prefix (e.g., `/api/customers`, `/api/contact`).
- Adjust frontend contact route to connect directly to the server, replacing gateway references with server URLs.

backend/server/src/main/java/dev/rheinsw/server/contact/controller/ContactController.java

@@ -19,7 +19,7 @@ import org.springframework.web.bind.annotation.RestController;
  */
 @RestController
 @AllArgsConstructor
-@RequestMapping("/contact")
+@RequestMapping("/api/contact")
 public class ContactController {
 
     private static final Logger log = LoggerFactory.getLogger(ContactController.class);

backend/server/src/main/java/dev/rheinsw/server/customer/controller/CustomerController.java

@@ -24,7 +24,7 @@ import java.util.UUID;
  * @since 02.07.25
  */
 @RestController
-@RequestMapping("/customers")
+@RequestMapping("/api/customers")
 @RequiredArgsConstructor
 public class CustomerController extends AbstractController {
 

backend/server/src/main/java/dev/rheinsw/server/mail/controller/MailController.java

@@ -14,7 +14,7 @@ import org.springframework.web.bind.annotation.RestController;
  * @since 04.05.25
  */
 @RestController
-@RequestMapping("/mail")
+@RequestMapping("/api/mail")
 @RequiredArgsConstructor
 public class MailController {
 

backend/server/src/main/java/dev/rheinsw/server/project/controller/ProjectController.java

@@ -23,7 +23,7 @@ import java.util.UUID;
  * @since 12.07.25
  */
 @RestController
-@RequestMapping("/projects")
+@RequestMapping("/api/projects")
 @RequiredArgsConstructor
 public class ProjectController extends AbstractController {
 

backend/server/src/main/resources/application.yml

@@ -1,5 +1,5 @@
 server:
-  port: 8081
+  port: 8080
 
 spring:
   application:
@@ -49,4 +49,4 @@ hcaptcha:
 logging:
   level:
     org.hibernate.SQL: ${LOG_SQL_LEVEL}
-    org.hibernate.type.descriptor.sql.BasicBinder: ${LOG_BINDER_LEVEL}
+    org.hibernate.type.descriptor.sql.BasicBinder: ${LOG_BINDER_LEVEL}