feat(training): add Paraglide i18n to training UI components and wire SegmentationTrainingCard

- Convert TrainingHistory, OcrTrainingCard, SegmentationTrainingCard, and
  TranscriptionBlock "Nur Segmentierung" badge to use Paraglide message keys
- Add availableSegBlocks to TrainingInfoResponse to expose segmentation
  block count in the training info endpoint
- Wire SegmentationTrainingCard into admin/system page below OCR training card
- Update api.ts with availableSegBlocks field

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

frontend/src/lib/components/OcrTrainingCard.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 import TrainingHistory from './TrainingHistory.svelte';
+import { m } from '$lib/paraglide/messages.js';
 
 interface Run {
 	id: string;
@@ -42,7 +43,7 @@ async function startTraining() {
 	try {
 		const res = await fetch('/api/ocr/train', { method: 'POST' });
 		if (res.ok) {
-			successMessage = 'Training wurde gestartet und abgeschlossen.';
+			successMessage = m.training_success();
 			setTimeout(() => {
 				successMessage = null;
 			}, 5000);
@@ -54,16 +55,14 @@ async function startTraining() {
 </script>
 
 <div class="rounded-sm border border-line bg-surface p-6 shadow-sm">
-	<h2 class="mb-1 font-sans text-sm font-bold text-ink">Kurrent-Erkennung trainieren</h2>
-	<p class="mb-4 text-sm text-ink-2">
-		Starte ein neues Training mit den bisher geprüften OCR-Blöcken, um die Erkennungsgenauigkeit für
-		Kurrentschrift zu verbessern.
-	</p>
+	<h2 class="mb-1 font-sans text-sm font-bold text-ink">{m.training_ocr_heading()}</h2>
+	<p class="mb-4 text-sm text-ink-2">{m.training_ocr_description()}</p>
 
 	<p class="mb-3 text-sm text-ink">
-		<strong>{available}</strong> geprüfte Blöcke bereit /
-		<strong>{trainingInfo?.availableDocuments ?? 0}</strong> Dokumente
-		<span class="text-ink-2">(von {trainingInfo?.totalOcrBlocks ?? 0} OCR-Blöcken gesamt)</span>
+		{m.training_ocr_blocks_ready({ blocks: available, docs: trainingInfo?.availableDocuments ?? 0 })}
+		<span class="text-ink-2"
+			>{m.training_ocr_blocks_total({ total: trainingInfo?.totalOcrBlocks ?? 0 })}</span
+		>
 	</p>
 
 	<button
@@ -71,21 +70,23 @@ async function startTraining() {
 		disabled={disabled}
 		class="rounded-sm bg-primary px-5 py-2 font-sans text-xs font-bold tracking-widest text-primary-fg uppercase transition-opacity hover:opacity-80 focus-visible:ring-2 focus-visible:ring-brand-navy disabled:cursor-not-allowed disabled:opacity-50"
 	>
-		{training ? '…' : 'Training starten'}
+		{training ? '…' : m.training_start_btn()}
 	</button>
 
 	{#if tooFewBlocks}
 		<p class="mt-2 text-xs text-ink-3">
-			Mindestens 5 geprüfte Blöcke erforderlich (aktuell: {available}).
+			{m.training_too_few_blocks({ available })}
 		</p>
 	{:else if serviceDown}
-		<p class="mt-2 text-xs text-orange-600">OCR-Dienst ist nicht erreichbar.</p>
+		<p class="mt-2 text-xs text-orange-600">{m.training_service_down()}</p>
 	{/if}
 
 	{#if successMessage}
 		<p class="mt-2 text-xs text-green-700">{successMessage}</p>
 	{/if}
 
-	<h3 class="mt-6 mb-3 text-xs font-bold tracking-widest text-ink-3 uppercase">Verlauf</h3>
+	<h3 class="mt-6 mb-3 text-xs font-bold tracking-widest text-ink-3 uppercase">
+		{m.training_history_heading()}
+	</h3>
 	<TrainingHistory runs={trainingInfo?.runs ?? []} />
 </div>