test(stammbaum): getFamilyNetwork excludes edges with non-family endpoints

Proves the in-memory filter correctly drops edges where one Person is
not in findAllFamilyMembers(), preventing non-family relationships from
leaking into the graph.

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

backend/src/test/java/org/raddatz/familienarchiv/relationship/RelationshipServiceTest.java

@@ -13,7 +13,10 @@ import org.raddatz.familienarchiv.relationship.dto.CreateRelationshipRequest;
 import org.raddatz.familienarchiv.service.PersonService;
 import org.springframework.dao.DataIntegrityViolationException;
 
+import org.raddatz.familienarchiv.relationship.dto.NetworkDTO;
+
 import java.time.Instant;
+import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
 
@@ -167,6 +170,27 @@ class RelationshipServiceTest {
                 .isEqualTo(ErrorCode.RELATIONSHIP_NOT_FOUND);
     }
 
+    @Test
+    void getFamilyNetwork_excludes_edges_where_one_endpoint_is_not_a_family_member() {
+        // alice and bob are family members; charlie is NOT (not in findAllFamilyMembers result).
+        // Two edges exist: alice→bob (both family) and alice→charlie (one non-family).
+        // Only the alice→bob edge must appear in the returned NetworkDTO.
+        UUID aliceBobRelId = UUID.randomUUID();
+        UUID aliceCharlieRelId = UUID.randomUUID();
+        PersonRelationship aliceBob = parentOf(alice, bob, aliceBobRelId);
+        PersonRelationship aliceCharlie = parentOf(alice, charlie, aliceCharlieRelId);
+
+        when(personService.findAllFamilyMembers()).thenReturn(List.of(alice, bob));
+        when(relationshipRepository.findAllByRelationTypeIn(any())).thenReturn(List.of(aliceBob, aliceCharlie));
+
+        NetworkDTO result = service.getFamilyNetwork();
+
+        assertThat(result.nodes()).hasSize(2);
+        assertThat(result.edges()).hasSize(1);
+        assertThat(result.edges().get(0).personId()).isEqualTo(alice.getId());
+        assertThat(result.edges().get(0).relatedPersonId()).isEqualTo(bob.getId());
+    }
+
     // --- helpers ---
 
     private static Person person(String name) {