feat(library): surface metadata enrichment status, errors and covers

The mapper dropped metadata_status and hardcoded availability, so enrichment
state was invisible and a just-uploaded track never appeared to change. Map
metadata_status/metadata_error/has_cover onto Track; add MetadataStatusBadge
(pending spinner / enriched / failed-with-reason / manual) shown in TrackRow,
and serve token-bearing track covers via getTrackCoverUrl.

UploadPage now polls each uploaded track (stops once enrichment settles) so the
resolved title/artist — or a failure reason — appears live. i18n in en + ru.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/track/MetadataStatusBadge.tsx

@@ -0,0 +1,47 @@
+import { Badge, Spinner, Tooltip } from '@olly/modern-sk';
+import { useTranslation } from 'react-i18next';
+import type { MetadataStatus } from '../../api/types';
+
+interface Props {
+  status: MetadataStatus;
+  /** Reason shown in the tooltip for a `failed` status. */
+  error?: string;
+  /** When true, render nothing for the normal `enriched` state (keeps dense
+   * track lists quiet; the upload screen sets this false to confirm success). */
+  hideWhenEnriched?: boolean;
+}
+
+type Variant = 'lime' | 'ember' | 'neutral' | 'outline';
+
+const VARIANT: Record<MetadataStatus, Variant> = {
+  pending: 'neutral',
+  enriched: 'lime',
+  failed: 'ember',
+  manual: 'outline',
+};
+
+/**
+ * Shows a track's metadata-enrichment state (distinct from file availability).
+ * `pending` carries a spinner; `failed` exposes the backend reason on hover.
+ */
+export function MetadataStatusBadge({
+  status,
+  error,
+  hideWhenEnriched = true,
+}: Props) {
+  const { t } = useTranslation();
+  if (status === 'enriched' && hideWhenEnriched) return null;
+
+  const label = t(`metadata.status.${status}`);
+  const tooltip =
+    status === 'failed' && error ? error : t(`metadata.statusHint.${status}`);
+
+  return (
+    <Tooltip content={tooltip}>
+      <Badge variant={VARIANT[status]} dot={status !== 'pending'}>
+        {status === 'pending' ? <Spinner size="sm" /> : null}
+        {label}
+      </Badge>
+    </Tooltip>
+  );
+}