refactor(transcription): split reorderBlocks for command-query separation

TranscriptionService.reorderBlocks() now returns void (command).
Controller calls listBlocks() separately after reorder (query).
Updated test to match new void signature.

Fixes @Felix: "reorderBlocks violates command-query separation"

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

backend/src/main/java/org/raddatz/familienarchiv/controller/TranscriptionBlockController.java

@@ -77,7 +77,8 @@ public class TranscriptionBlockController {
     public List<TranscriptionBlock> reorderBlocks(
             @PathVariable UUID documentId,
             @RequestBody ReorderTranscriptionBlocksDTO dto) {
-        return transcriptionService.reorderBlocks(documentId, dto);
+        transcriptionService.reorderBlocks(documentId, dto);
+        return transcriptionService.listBlocks(documentId);
     }
 
     @GetMapping("/{blockId}/history")

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

@@ -107,14 +107,13 @@ public class TranscriptionService {
     }
 
     @Transactional
-    public List<TranscriptionBlock> reorderBlocks(UUID documentId, ReorderTranscriptionBlocksDTO dto) {
+    public void reorderBlocks(UUID documentId, ReorderTranscriptionBlocksDTO dto) {
         List<UUID> blockIds = dto.getBlockIds();
         for (int i = 0; i < blockIds.size(); i++) {
             TranscriptionBlock block = getBlock(documentId, blockIds.get(i));
             block.setSortOrder(i);
             blockRepository.save(block);
         }
-        return blockRepository.findByDocumentIdOrderBySortOrderAsc(documentId);
     }
 
     public List<TranscriptionBlockVersion> getBlockHistory(UUID documentId, UUID blockId) {

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

@@ -184,7 +184,6 @@ class TranscriptionServiceTest {
         when(blockRepository.findByIdAndDocumentId(id2, docId)).thenReturn(Optional.of(block2));
         when(blockRepository.findByIdAndDocumentId(id1, docId)).thenReturn(Optional.of(block1));
         when(blockRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
-        when(blockRepository.findByDocumentIdOrderBySortOrderAsc(docId)).thenReturn(List.of(block2, block1));
 
         ReorderTranscriptionBlocksDTO dto = new ReorderTranscriptionBlocksDTO(List.of(id2, id1));