feat(flutter): admin DTOs (request, quarantine item, user, invite)

Hand-rolled to match the server's actual JSON shapes:
- AdminRequest carries user_id (UUID, not username); kind switches
  which title field is the display name
- AdminQuarantineItem aggregates reports per track with reason_counts
  and a nested reports[] list, mirroring adminQueueRowView
- AdminUser includes display_name + auto_approve_requests
- Invite uses invited_by UUID + note (server hardcodes 24h TTL)

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

flutter_client/lib/models/admin_quarantine_item.dart

@@ -0,0 +1,92 @@
+/// One user's report under an aggregated quarantine row.
+class AdminQuarantineReport {
+  const AdminQuarantineReport({
+    required this.userId,
+    required this.username,
+    required this.reason,
+    this.notes,
+    required this.createdAt,
+  });
+
+  final String userId;
+  final String username;
+  final String reason;
+  final String? notes;
+  final String createdAt;
+
+  factory AdminQuarantineReport.fromJson(Map<String, dynamic> j) =>
+      AdminQuarantineReport(
+        userId: j['user_id'] as String? ?? '',
+        username: j['username'] as String? ?? '',
+        reason: j['reason'] as String? ?? '',
+        notes: j['notes'] as String?,
+        createdAt: j['created_at'] as String? ?? '',
+      );
+}
+
+/// Mirrors `adminQueueRowView` from internal/api/admin_quarantine.go.
+/// One row aggregates all reports against a single track, with
+/// per-reason counts and the underlying per-user reports nested.
+class AdminQuarantineItem {
+  const AdminQuarantineItem({
+    required this.trackId,
+    required this.trackTitle,
+    required this.artistName,
+    required this.albumTitle,
+    required this.albumId,
+    this.lidarrAlbumMbid,
+    required this.reportCount,
+    required this.latestAt,
+    required this.reasonCounts,
+    required this.reports,
+  });
+
+  final String trackId;
+  final String trackTitle;
+  final String artistName;
+  final String albumTitle;
+  final String albumId;
+  final String? lidarrAlbumMbid;
+  final int reportCount;
+  final String latestAt;
+
+  /// Map of reason → number of reports citing that reason.
+  final Map<String, int> reasonCounts;
+
+  final List<AdminQuarantineReport> reports;
+
+  /// One-line summary of the most-cited reason. Returns "<top>" when
+  /// only one reason exists or "<top> (+N more)" when there are
+  /// additional distinct reasons.
+  String get topReasonSummary {
+    if (reasonCounts.isEmpty) return '';
+    final entries = reasonCounts.entries.toList()
+      ..sort((a, b) => b.value.compareTo(a.value));
+    final top = entries.first.key;
+    return entries.length > 1
+        ? '$top (+${entries.length - 1} more)'
+        : top;
+  }
+
+  factory AdminQuarantineItem.fromJson(Map<String, dynamic> j) {
+    final reasonCountsRaw =
+        (j['reason_counts'] as Map?)?.cast<String, dynamic>() ?? const {};
+    final reportsRaw = (j['reports'] as List?) ?? const [];
+    return AdminQuarantineItem(
+      trackId: j['track_id'] as String? ?? '',
+      trackTitle: j['track_title'] as String? ?? '',
+      artistName: j['artist_name'] as String? ?? '',
+      albumTitle: j['album_title'] as String? ?? '',
+      albumId: j['album_id'] as String? ?? '',
+      lidarrAlbumMbid: j['lidarr_album_mbid'] as String?,
+      reportCount: (j['report_count'] as int?) ?? 0,
+      latestAt: j['latest_at'] as String? ?? '',
+      reasonCounts:
+          reasonCountsRaw.map((k, v) => MapEntry(k, (v as int?) ?? 0)),
+      reports: reportsRaw
+          .map((e) =>
+              AdminQuarantineReport.fromJson((e as Map).cast<String, dynamic>()))
+          .toList(growable: false),
+    );
+  }
+}