refactor(user): migrate UserController to @RequiredArgsConstructor + final fields

The circular-dependency that originally forced @AllArgsConstructor was
removed when changePassword orchestration moved into the controller.
No cycle now exists between UserController, UserService, AuthService,
or AuditService — final fields and constructor injection are safe again.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/user/UserController.java

@@ -30,15 +30,15 @@ import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.ResponseStatus;
 import org.springframework.web.bind.annotation.RestController;
 
-import lombok.AllArgsConstructor;
+import lombok.RequiredArgsConstructor;
 
 @RestController
 @RequestMapping("/api/")
-@AllArgsConstructor
+@RequiredArgsConstructor
 public class UserController {
-    private UserService userService;
-    private AuthService authService;
-    private AuditService auditService;
+    private final UserService userService;
+    private final AuthService authService;
+    private final AuditService auditService;
 
     @GetMapping("users/me")
     public ResponseEntity<AppUser> getCurrentUser(Authentication authentication) {