feat(flutter): SystemPlaylistsStatus model + endpoint method

Adds the model + MeApi.systemPlaylistsStatus() for the home Playlists
row's placeholder-variant logic (building / failed / pending /
seed-needed). Mirrors GET /api/me/system-playlists-status which
returns the caller's most recent system_playlist_runs row.

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

flutter_client/lib/api/endpoints/me.dart

@@ -2,6 +2,7 @@ import 'package:dio/dio.dart';
 
 import '../../models/history_event.dart';
 import '../../models/quarantine_mine.dart';
+import '../../models/system_playlists_status.dart';
 
 /// /api/me/* endpoints — caller-scoped data (history, profile, etc.).
 class MeApi {
@@ -27,4 +28,14 @@ class MeApi {
             QuarantineMineRow.fromJson((e as Map).cast<String, dynamic>()))
         .toList(growable: false);
   }
+
+  /// GET /api/me/system-playlists-status. Returns the caller's most
+  /// recent system-playlist build state. Used by the home Playlists
+  /// row to choose between real and placeholder cards.
+  Future<SystemPlaylistsStatus> systemPlaylistsStatus() async {
+    final r = await _dio.get<Map<String, dynamic>>(
+      '/api/me/system-playlists-status',
+    );
+    return SystemPlaylistsStatus.fromJson(r.data ?? const {});
+  }
 }

flutter_client/lib/models/system_playlists_status.dart

@@ -0,0 +1,24 @@
+/// Mirrors `systemPlaylistsStatusResp` from internal/api/me_system_playlists.go.
+/// Reflects the caller's most recent system_playlist_runs row, or zero
+/// values when no row exists yet (the user has never had a build attempted).
+class SystemPlaylistsStatus {
+  const SystemPlaylistsStatus({
+    required this.inFlight,
+    this.lastRunAt,
+    this.lastError,
+  });
+
+  final bool inFlight;
+  final String? lastRunAt;
+  final String? lastError;
+
+  factory SystemPlaylistsStatus.empty() =>
+      const SystemPlaylistsStatus(inFlight: false);
+
+  factory SystemPlaylistsStatus.fromJson(Map<String, dynamic> j) =>
+      SystemPlaylistsStatus(
+        inFlight: j['in_flight'] as bool? ?? false,
+        lastRunAt: j['last_run_at'] as String?,
+        lastError: j['last_error'] as String?,
+      );
+}