refactor(geschichte): introduce GeschichteQueryService with existsById()

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

backend/src/main/java/org/raddatz/familienarchiv/geschichte/GeschichteQueryService.java

@@ -0,0 +1,23 @@
+package org.raddatz.familienarchiv.geschichte;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+
+import java.util.UUID;
+
+/**
+ * Thin read-only service owning {@link GeschichteRepository}.
+ * Exists so that {@code JourneyItemService} can check Geschichte existence
+ * without holding a direct reference to the Geschichte repository
+ * (cross-domain repository access is not allowed per layering rules).
+ */
+@Service
+@RequiredArgsConstructor
+public class GeschichteQueryService {
+
+    private final GeschichteRepository geschichteRepository;
+
+    public boolean existsById(UUID id) {
+        return geschichteRepository.existsById(id);
+    }
+}

backend/src/test/java/org/raddatz/familienarchiv/geschichte/GeschichteQueryServiceTest.java

@@ -0,0 +1,38 @@
+package org.raddatz.familienarchiv.geschichte;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class GeschichteQueryServiceTest {
+
+    @Mock
+    GeschichteRepository geschichteRepository;
+
+    @InjectMocks
+    GeschichteQueryService geschichteQueryService;
+
+    @Test
+    void existsById_returns_true_when_geschichte_exists() {
+        UUID id = UUID.randomUUID();
+        when(geschichteRepository.existsById(id)).thenReturn(true);
+
+        assertThat(geschichteQueryService.existsById(id)).isTrue();
+    }
+
+    @Test
+    void existsById_returns_false_when_geschichte_does_not_exist() {
+        UUID id = UUID.randomUUID();
+        when(geschichteRepository.existsById(id)).thenReturn(false);
+
+        assertThat(geschichteQueryService.existsById(id)).isFalse();
+    }
+}