fix(training): count segmentation blocks regardless of text content

The findSegmentationBlocks query was filtering out blocks with non-empty
text. Segmentation training only needs annotation geometry (polygon/bbox),
not transcription text — so any MANUAL block on a KURRENT_SEGMENTATION
document should count, regardless of whether it has text.

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

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

@@ -31,7 +31,7 @@ public interface TranscriptionBlockRepository extends JpaRepository<Transcriptio
             SELECT b FROM TranscriptionBlock b
             JOIN DocumentAnnotation a ON a.id = b.annotationId
             JOIN Document d ON d.id = b.documentId
-            WHERE b.source = 'MANUAL' AND (b.text IS NULL OR b.text = '')
+            WHERE b.source = 'MANUAL'
             AND 'KURRENT_SEGMENTATION' MEMBER OF d.trainingLabels
             """)
     List<TranscriptionBlock> findSegmentationBlocks();