fix(transcription): persist mentionedPersons on block update; eager-load collection

TranscriptionService.updateBlock was not writing mentionedPersons from the DTO
back to the entity, so @mentions were lost on every save. Clear-then-addAll
pattern avoids Hibernate orphan issues with @ElementCollection.

Switch @ElementCollection fetch to EAGER so callers can read mentionedPersons
outside an active transaction without a LazyInitializationException.

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

backend/src/main/java/org/raddatz/familienarchiv/model/TranscriptionBlock.java

@@ -35,7 +35,7 @@ public class TranscriptionBlock {
     @Column(columnDefinition = "TEXT")
     private String text;
 
-    @ElementCollection(fetch = FetchType.LAZY)
+    @ElementCollection(fetch = FetchType.EAGER)
     @CollectionTable(
             name = "transcription_block_mentioned_persons",
             joinColumns = @JoinColumn(name = "block_id"))

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

@@ -134,6 +134,8 @@ public class TranscriptionService {
         if (dto.getLabel() != null) {
             block.setLabel(dto.getLabel());
         }
+        block.getMentionedPersons().clear();
+        block.getMentionedPersons().addAll(dto.getMentionedPersons());
         block.setUpdatedBy(userId);
 
         TranscriptionBlock saved = blockRepository.save(block);

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

@@ -17,6 +17,7 @@ import org.raddatz.familienarchiv.model.BlockSource;
 import org.raddatz.familienarchiv.model.Document;
 import org.raddatz.familienarchiv.model.DocumentAnnotation;
 import org.raddatz.familienarchiv.model.Person;
+import org.raddatz.familienarchiv.model.PersonMention;
 import org.raddatz.familienarchiv.model.ScriptType;
 import org.raddatz.familienarchiv.model.TranscriptionBlock;
 import org.raddatz.familienarchiv.model.TranscriptionBlockVersion;
@@ -215,6 +216,31 @@ class TranscriptionServiceTest {
         assertThat(result.getSource()).isEqualTo(BlockSource.MANUAL);
     }
 
+    @Test
+    void updateBlock_replacesMentionedPersonsFromDto() {
+        UUID docId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+        UUID personId = UUID.randomUUID();
+
+        TranscriptionBlock block = TranscriptionBlock.builder()
+                .id(blockId).documentId(docId).text("old").build();
+        when(blockRepository.findByIdAndDocumentId(blockId, docId)).thenReturn(Optional.of(block));
+        when(blockRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+        when(documentService.getDocumentById(any())).thenReturn(
+                Document.builder().scriptType(ScriptType.TYPEWRITER).build());
+
+        PersonMention mention = new PersonMention(personId, "Auguste");
+        UpdateTranscriptionBlockDTO dto = UpdateTranscriptionBlockDTO.builder()
+                .text("@Auguste text")
+                .mentionedPersons(List.of(mention))
+                .build();
+
+        TranscriptionBlock result = transcriptionService.updateBlock(docId, blockId, dto, UUID.randomUUID());
+
+        assertThat(result.getMentionedPersons())
+                .containsExactly(mention);
+    }
+
     @Test
     void updateBlock_triggersTraining_whenKurrentSenderPresent() {
         UUID docId = UUID.randomUUID();