fix(frontend): accessibility fixes for TrainingHistory expand/collapse and FAILED badge

- Add aria-expanded + aria-controls to expand button (WCAG 4.1.2)
- Add id="training-history-rows" to tbody for aria-controls target
- Replace title= tooltip on FAILED badge with details/summary for keyboard
  and touch accessibility; add training_error_detail_label i18n key
- Use motion-safe:animate-pulse on RUNNING badge for prefers-reduced-motion

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

frontend/messages/de.json

@@ -558,6 +558,7 @@
 	"training_history_col_cer": "Fehlerrate",
 	"training_status_done": "Fertig",
 	"training_status_failed": "Fehler",
+	"training_error_detail_label": "Fehlerdetails",
 	"training_status_running": "Läuft…",
 	"training_seg_heading": "Segmentierung trainieren",
 	"training_seg_description": "Starte ein neues Training mit annotierten Segmentierungsbereichen, um die Texterkennung zu verbessern.",

frontend/messages/en.json

@@ -558,6 +558,7 @@
 	"training_history_col_cer": "Error Rate",
 	"training_status_done": "Done",
 	"training_status_failed": "Failed",
+	"training_error_detail_label": "Error details",
 	"training_status_running": "Running…",
 	"training_seg_heading": "Train segmentation",
 	"training_seg_description": "Start a new training run using annotated segmentation regions to improve text detection.",

frontend/messages/es.json

@@ -558,6 +558,7 @@
 	"training_history_col_cer": "Tasa de error",
 	"training_status_done": "Listo",
 	"training_status_failed": "Error",
+	"training_error_detail_label": "Detalles del error",
 	"training_status_running": "Ejecutando…",
 	"training_seg_heading": "Entrenar segmentación",
 	"training_seg_description": "Inicia un nuevo entrenamiento con regiones de segmentación anotadas para mejorar la detección de texto.",

frontend/src/lib/components/TrainingHistory.svelte

@@ -52,7 +52,7 @@ function formatCer(cer: number | undefined | null): string {
 			<th class="hidden pb-2 text-right md:table-cell">{m.training_history_col_cer()}</th>
 		</tr>
 	</thead>
-	<tbody>
+	<tbody id="training-history-rows">
 		{#if runs.length === 0}
 			<tr>
 				<td colspan="5" class="py-4 text-center text-sm text-ink-2">
@@ -85,7 +85,6 @@ function formatCer(cer: number | undefined | null): string {
 						{:else if run.status === 'FAILED'}
 							<span
 								class="inline-flex items-center gap-1 rounded-sm bg-red-100 px-1.5 py-0.5 text-xs font-medium text-red-700"
-								title={run.errorMessage}
 							>
 								<svg
 									aria-hidden="true"
@@ -101,13 +100,21 @@ function formatCer(cer: number | undefined | null): string {
 								</svg>
 								{m.training_status_failed()}
 							</span>
+							{#if run.errorMessage}
+								<details class="mt-0.5">
+									<summary class="cursor-pointer text-xs text-red-700 underline">
+										{m.training_error_detail_label()}
+									</summary>
+									<p class="mt-1 text-xs text-red-600">{run.errorMessage}</p>
+								</details>
+							{/if}
 						{:else}
 							<span
 								class="inline-flex items-center gap-1 rounded-sm bg-yellow-100 px-1.5 py-0.5 text-xs font-medium text-yellow-700"
 							>
 								<span
 									aria-hidden="true"
-									class="h-1.5 w-1.5 animate-pulse rounded-full bg-yellow-500"
+									class="h-1.5 w-1.5 rounded-full bg-yellow-500 motion-safe:animate-pulse"
 								></span>
 								{m.training_status_running()}
 							</span>
@@ -128,6 +135,8 @@ function formatCer(cer: number | undefined | null): string {
 	<div class="mt-2 text-center">
 		<button
 			type="button"
+			aria-expanded={expanded}
+			aria-controls="training-history-rows"
 			class="text-xs font-medium text-ink-3 transition-colors hover:text-ink"
 			onclick={() => (expanded = !expanded)}
 		>