feat(training): add document-level training enrollment

- V29 migration: document_training_labels join table
- TrainingLabel enum: KURRENT_RECOGNITION, KURRENT_SEGMENTATION
- Document.trainingLabels @ElementCollection
- DocumentService.addTrainingLabel / removeTrainingLabel
- PATCH /api/documents/{id}/training-labels (WRITE_ALL)
- Auto-enroll on Kurrent OCR trigger (OcrService.startOcr)
- TranscriptionEditView: enrollment chips in panel footer
- JPQL queries updated to use MEMBER OF trainingLabels

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

frontend/src/routes/documents/[id]/+page.svelte

@@ -129,6 +129,15 @@ async function reviewToggle(blockId: string) {
 	transcriptionBlocks = transcriptionBlocks.map((b) => (b.id === blockId ? updated : b));
 }
 
+async function toggleTrainingLabel(label: string, enrolled: boolean) {
+	const res = await fetch(`/api/documents/${doc.id}/training-labels`, {
+		method: 'PATCH',
+		headers: { 'Content-Type': 'application/json' },
+		body: JSON.stringify({ label, enrolled })
+	});
+	if (!res.ok) throw new Error('Failed to update training label');
+}
+
 let ocrRunning = $state(false);
 let ocrProgressMessage = $state('');
 let ocrErrorMessage = $state('');
@@ -449,11 +458,14 @@ onMount(() => {
 							activeAnnotationId={activeAnnotationId}
 							storedScriptType={doc.scriptType ?? ''}
 							canRunOcr={canWrite && !!doc.filePath}
+							canWrite={canWrite}
+							trainingLabels={doc.trainingLabels ?? []}
 							onBlockFocus={handleBlockFocus}
 							onSaveBlock={saveBlock}
 							onDeleteBlock={deleteBlock}
 							onReviewToggle={reviewToggle}
 							onTriggerOcr={triggerOcr}
+							onToggleTrainingLabel={toggleTrainingLabel}
 						/>
 					{/if}
 				</div>