feat(notifications): add documentTitle to NotificationDTO via DocumentService lookup

Notification rows in the history page need the document title. Added
findTitlesByIds(Collection<UUID>) to DocumentService (one query via a new
JPQL projection on DocumentRepository). NotificationService.getNotifications()
now fetches all titles for the page in a single extra query and maps them into
the DTO. documentTitle is null when the document has been deleted.

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

backend/src/main/java/org/raddatz/familienarchiv/dto/NotificationDTO.java

@@ -14,5 +14,6 @@ public record NotificationDTO(
         UUID annotationId,
         @Schema(requiredMode = Schema.RequiredMode.REQUIRED) boolean read,
         @Schema(requiredMode = Schema.RequiredMode.REQUIRED) LocalDateTime createdAt,
-        String actorName
+        String actorName,
+        String documentTitle
 ) {}

backend/src/main/java/org/raddatz/familienarchiv/repository/DocumentRepository.java

@@ -12,7 +12,9 @@ import org.springframework.data.repository.query.Param;
 import org.springframework.stereotype.Repository;
 
 import java.time.LocalDate;
+import java.util.Collection;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.UUID;
 
@@ -44,6 +46,9 @@ public interface DocumentRepository extends JpaRepository<Document, UUID>, JpaSp
 
     List<Document> findByFileHashIsNullAndFilePathIsNotNull();
 
+    @Query("SELECT d.id, d.title FROM Document d WHERE d.id IN :ids")
+    List<Object[]> findIdAndTitleByIdIn(@Param("ids") Collection<UUID> ids);
+
     long countByMetadataCompleteFalse();
 
     List<Document> findByMetadataCompleteFalse(Sort sort);

backend/src/main/java/org/raddatz/familienarchiv/service/DocumentService.java

@@ -25,8 +25,11 @@ import java.security.NoSuchAlgorithmException;
 import java.time.LocalDate;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 import java.util.UUID;
@@ -46,6 +49,15 @@ public class DocumentService {
 
     public record StoreResult(Document document, boolean isNew) {}
 
+    public Map<UUID, String> findTitlesByIds(Collection<UUID> ids) {
+        if (ids.isEmpty()) return Map.of();
+        Map<UUID, String> titles = new HashMap<>();
+        for (Object[] row : documentRepository.findIdAndTitleByIdIn(ids)) {
+            titles.put((UUID) row[0], (String) row[1]);
+        }
+        return titles;
+    }
+
     /**
      * Lädt eine Datei hoch.
      * - Prüft, ob ein Eintrag (aus Excel) schon existiert.

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

@@ -75,7 +75,7 @@ class NotificationControllerTest {
         AppUser user = AppUser.builder().id(USER_ID).username("testuser").build();
         NotificationDTO dto = new NotificationDTO(
                 UUID.randomUUID(), NotificationType.REPLY, UUID.randomUUID(),
-                UUID.randomUUID(), null, false, LocalDateTime.now(), "Anna Smith");
+                UUID.randomUUID(), null, false, LocalDateTime.now(), "Anna Smith", "Testdokument");
 
         when(userService.findByUsername("testuser")).thenReturn(user);
         when(notificationService.getNotifications(eq(USER_ID), any(), any(), any()))
@@ -123,6 +123,20 @@ class NotificationControllerTest {
                 .andExpect(status().isBadRequest());
     }
 
+    @Test
+    @WithMockUser(username = "testuser", authorities = {"READ_ALL"})
+    void getNotifications_returns400_whenSizeExceedsMaximum() throws Exception {
+        mockMvc.perform(get("/api/notifications").param("size", "200"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser(username = "testuser", authorities = {"READ_ALL"})
+    void getNotifications_returns400_whenSizeIsZero() throws Exception {
+        mockMvc.perform(get("/api/notifications").param("size", "0"))
+                .andExpect(status().isBadRequest());
+    }
+
     // ─── POST /api/notifications/read-all ────────────────────────────────────
 
     @Test