feat(android): Hidden tab — cover thumb + relative-time stamp

Audit v2 #12. Hidden rows were text-only ("title", "artist · album",
reason chip); Flutter shows the album cover thumbnail and a "3h ago"
relative-time stamp next to the reason. Both added to QuarantineRef
(coverUrl computed from albumId) and HiddenRow renders them.

Time helper is duplicated from HistoryTab inline rather than
hoisted — both copies are small and screen-private; a shared
RelativeTime widget can land later if a third caller surfaces.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/fabledsword/minstrel/models/QuarantineRef.kt

@@ -28,4 +28,13 @@ data class QuarantineRef(
             "duplicate" -> "Duplicate"
             else -> "Other"
         }
+
+    /**
+     * Cover URL derived from the parent album's
+     * `/api/albums/{id}/cover` endpoint. Uses the placeholder host
+     * that `BaseUrlInterceptor` rewrites to the live server URL.
+     * Empty when the row has no album binding (rare).
+     */
+    val coverUrl: String
+        get() = if (albumId.isEmpty()) "" else "http://placeholder.invalid/api/albums/$albumId/cover"
 }

android/app/src/main/java/com/fabledsword/minstrel/quarantine/ui/HiddenTab.kt

@@ -29,6 +29,7 @@ import com.composables.icons.lucide.Lucide
 import com.fabledsword.minstrel.models.QuarantineRef
 import com.fabledsword.minstrel.shared.widgets.EmptyState
 import com.fabledsword.minstrel.shared.widgets.PullToRefreshScaffold
+import com.fabledsword.minstrel.shared.widgets.TrackCoverThumb
 
 @Composable
 fun HiddenTab(viewModel: HiddenTabViewModel = hiltViewModel()) {
@@ -73,6 +74,7 @@ private fun HiddenRow(row: QuarantineRef, onUnflag: () -> Unit) {
         verticalAlignment = Alignment.CenterVertically,
         horizontalArrangement = Arrangement.spacedBy(12.dp),
     ) {
+        TrackCoverThumb(coverUrl = row.coverUrl, contentDescription = row.trackTitle)
         Column(modifier = Modifier.weight(1f)) {
             Text(
                 text = row.trackTitle,
@@ -88,12 +90,24 @@ private fun HiddenRow(row: QuarantineRef, onUnflag: () -> Unit) {
                 maxLines = 1,
                 overflow = TextOverflow.Ellipsis,
             )
-            AssistChip(
-                onClick = {},
-                enabled = false,
-                label = { Text(row.reasonLabel) },
+            Row(
+                verticalAlignment = Alignment.CenterVertically,
+                horizontalArrangement = Arrangement.spacedBy(8.dp),
                 modifier = Modifier.padding(top = 4.dp),
-            )
+            ) {
+                AssistChip(
+                    onClick = {},
+                    enabled = false,
+                    label = { Text(row.reasonLabel) },
+                )
+                if (row.createdAt.isNotEmpty()) {
+                    Text(
+                        text = relativeTime(row.createdAt),
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    )
+                }
+            }
         }
         IconButton(onClick = onUnflag) {
             Icon(
@@ -111,3 +125,36 @@ private fun LoadingCentered() {
         CircularProgressIndicator(color = MaterialTheme.colorScheme.primary)
     }
 }
+
+// ─── Time helper (duplicated from HistoryTab to keep the widget local) ──
+
+private const val MINUTES_PER_HOUR = 60L
+private const val HOURS_PER_DAY = 24L
+private const val DAYS_PER_WEEK = 7L
+
+private fun relativeTime(iso: String): String {
+    val parsed = runCatching { java.time.OffsetDateTime.parse(iso) }.getOrNull()
+        ?: return iso
+    val local = parsed.atZoneSameInstant(java.time.ZoneId.systemDefault())
+    val now = java.time.OffsetDateTime.now(java.time.ZoneId.systemDefault())
+    val minutes = java.time.temporal.ChronoUnit.MINUTES.between(local, now)
+    val hours = java.time.temporal.ChronoUnit.HOURS.between(local, now)
+    val days = java.time.temporal.ChronoUnit.DAYS.between(local, now)
+    return when {
+        minutes < MINUTES_PER_HOUR -> "${minutes.coerceAtLeast(1)}m ago"
+        hours < HOURS_PER_DAY -> "${hours}h ago"
+        days < DAYS_PER_WEEK -> {
+            val dow = local.dayOfWeek.getDisplayName(
+                java.time.format.TextStyle.SHORT,
+                java.util.Locale.getDefault(),
+            )
+            val time = local.toLocalTime()
+                .format(java.time.format.DateTimeFormatter.ofPattern("HH:mm"))
+            "$dow $time"
+        }
+        else -> {
+            val pattern = if (local.year == now.year) "MMM d" else "MMM d, yyyy"
+            local.toLocalDate().format(java.time.format.DateTimeFormatter.ofPattern(pattern))
+        }
+    }
+}