refactor: centralise session key format in SessionKeys utility

backend/src/main/java/com/vaessl/app/search/SearchController.java

@@ -9,6 +9,7 @@ import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RestController;
 
+import com.vaessl.app.connection.SessionKeys;
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpSession;
 import jakarta.validation.Valid;
@@ -30,7 +31,7 @@ public class SearchController {
             @PageableDefault(size = 20) Pageable pageable, HttpServletRequest httpReq) {
         HttpSession session = httpReq.getSession(false);
         if (session == null
-                || session.getAttribute(request.serviceType() + "_CONNECTION_ID") == null) {
+                || session.getAttribute(SessionKeys.connectionId(request.serviceType())) == null) {
             return ResponseEntity.status(HttpStatus.UNAUTHORIZED).build();
         }