refactor: consolidate test mock constants into shared Mockdata class

Moved Mockdata from the connection package to the root test package and
extended it with MOCK_USER, MOCK_PASS, MOCK_TITLE, and MOCK_DESCRIPTION
so all test modules share a single source of truth. Removed duplicate
inline constants from ConnectionControllerTest, HomeboxIntegrationTest,
and SearchControllerTest.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

backend/src/test/java/com/vaessl/app/connection/ConnectionServiceTest.java

@@ -1,5 +1,6 @@
 package com.vaessl.app.connection;
 
+import static com.vaessl.app.Mockdata.*;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.doThrow;
@@ -17,8 +18,6 @@ import org.mockito.junit.jupiter.MockitoExtension;
 
 import com.vaessl.app.exception.EmptyCredentialsException;
 
-import static com.vaessl.app.connection.Mockdata.*;
-
 @ExtendWith(MockitoExtension.class)
 class ConnectionServiceTest {