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);