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/lib/components/TranscriptionEditView.svelte

@@ -20,6 +20,9 @@ type Props = {
 	onDeleteBlock: (blockId: string) => Promise<void>;
 	onReviewToggle: (blockId: string) => Promise<void>;
 	onTriggerOcr?: (scriptType: string) => void;
+	canWrite?: boolean;
+	trainingLabels?: string[];
+	onToggleTrainingLabel?: (label: string, enrolled: boolean) => Promise<void>;
 };
 
 let {
@@ -34,10 +37,14 @@ let {
 	onSaveBlock,
 	onDeleteBlock,
 	onReviewToggle,
-	onTriggerOcr
+	onTriggerOcr,
+	canWrite = false,
+	trainingLabels = [],
+	onToggleTrainingLabel
 }: Props = $props();
 
 let activeBlockId: string | null = $state(null);
+let localLabels: string[] = $derived.by(() => [...trainingLabels]);
 
 // Sync: when an annotation is clicked on the PDF, activate the corresponding block
 $effect(() => {
@@ -188,7 +195,7 @@ let dropTargetIdx: number | null = $state(null);
 let dragOffsetY: number = $state(0);
 let dragStartY = 0;
 let capturedEl: HTMLElement | null = null;
-let listEl: HTMLElement | null = null;
+let listEl: HTMLElement | null = $state(null);
 
 function handleGripDown(e: PointerEvent, blockId: string) {
 	if (!(e.target as HTMLElement).closest('[data-drag-handle]')) return;
@@ -240,6 +247,23 @@ function handlePointerUp() {
 	capturedEl = null;
 }
 
+async function handleLabelToggle(label: string) {
+	if (!onToggleTrainingLabel) return;
+	const enrolled = !localLabels.includes(label);
+	// Optimistic update
+	if (enrolled) {
+		localLabels = [...localLabels, label];
+	} else {
+		localLabels = localLabels.filter((l) => l !== label);
+	}
+	try {
+		await onToggleTrainingLabel(label, enrolled);
+	} catch {
+		// Revert on failure
+		localLabels = [...trainingLabels];
+	}
+}
+
 function flushViaBeacon() {
 	for (const [blockId, text] of pendingTexts) {
 		clearDebounce(blockId);
@@ -390,4 +414,23 @@ $effect(() => {
 			{/if}
 		</div>
 	{/if}
+
+	{#if canWrite}
+		<div class="border-t border-line px-4 py-3">
+			<p class="mb-2 font-sans text-xs font-medium text-ink-2">Für Training vormerken</p>
+			<div class="flex flex-wrap gap-2">
+				{#each [{ label: 'KURRENT_RECOGNITION', display: 'Kurrent-Erkennung' }, { label: 'KURRENT_SEGMENTATION', display: 'Segmentierung' }] as chip (chip.label)}
+					<button
+						type="button"
+						onclick={() => handleLabelToggle(chip.label)}
+						class="rounded-full border px-3 py-1 font-sans text-xs font-medium transition-colors {localLabels.includes(chip.label)
+							? 'border-brand-mint bg-brand-mint text-brand-navy'
+							: 'border-line bg-surface text-ink-3 hover:border-brand-mint hover:text-brand-navy'}"
+					>
+						{chip.display}
+					</button>
+				{/each}
+			</div>
+		</div>
+	{/if}
 </div>