feat(backend): add received-documents endpoint for persons

Add findByReceiversId to DocumentRepository, getDocumentsByReceiver
to DocumentService, and GET /api/persons/{id}/received-documents
to PersonController. Tests added for both service and controller layers.

Closes #1
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/controller/PersonControllerTest.java

@@ -0,0 +1,52 @@
+package org.raddatz.familienarchiv.controller;
+
+import org.junit.jupiter.api.Test;
+import org.raddatz.familienarchiv.model.Document;
+import org.raddatz.familienarchiv.security.PermissionAspect;
+import org.raddatz.familienarchiv.service.CustomUserDetailsService;
+import org.raddatz.familienarchiv.service.DocumentService;
+import org.raddatz.familienarchiv.service.PersonService;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.webmvc.test.autoconfigure.WebMvcTest;
+import org.raddatz.familienarchiv.config.SecurityConfig;
+import org.springframework.boot.autoconfigure.aop.AopAutoConfiguration;
+import org.springframework.context.annotation.Import;
+import org.springframework.security.test.context.support.WithMockUser;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+import org.springframework.test.web.servlet.MockMvc;
+
+import java.util.Collections;
+import java.util.UUID;
+
+import static org.mockito.Mockito.when;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+@WebMvcTest(PersonController.class)
+@Import({SecurityConfig.class, PermissionAspect.class, AopAutoConfiguration.class})
+class PersonControllerTest {
+
+    @Autowired MockMvc mockMvc;
+
+    @MockitoBean PersonService personService;
+    @MockitoBean DocumentService documentService;
+    @MockitoBean CustomUserDetailsService customUserDetailsService;
+
+    // ─── GET /api/persons/{id}/received-documents ─────────────────────────────
+
+    @Test
+    void getReceivedDocuments_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(get("/api/persons/{id}/received-documents", UUID.randomUUID()))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser
+    void getReceivedDocuments_returns200_whenAuthenticated() throws Exception {
+        UUID personId = UUID.randomUUID();
+        when(documentService.getDocumentsByReceiver(personId)).thenReturn(Collections.emptyList());
+
+        mockMvc.perform(get("/api/persons/{id}/received-documents", personId))
+                .andExpect(status().isOk());
+    }
+}

backend/src/test/java/org/raddatz/familienarchiv/service/DocumentServiceTest.java

@@ -121,4 +121,15 @@ class DocumentServiceTest {
         assertThat(result).isEqualTo(saved);
         verify(documentRepository).save(any());
     }
+
+    // ─── getDocumentsByReceiver ───────────────────────────────────────────────
+
+    @Test
+    void getDocumentsByReceiver_returnsDocumentsWherePersonIsReceiver() {
+        UUID receiverId = UUID.randomUUID();
+        Document doc = Document.builder().id(UUID.randomUUID()).title("Test").build();
+        when(documentRepository.findByReceiversId(receiverId)).thenReturn(List.of(doc));
+
+        assertThat(documentService.getDocumentsByReceiver(receiverId)).containsExactly(doc);
+    }
 }