Add Worker service with isolated task management and integrate into app

finlog_app/fluttery/lib/worker.dart

@@ -0,0 +1,47 @@
+import 'dart:async';
+import 'package:fluttery/fluttery.dart';
+
+abstract class Worker extends Service {
+  Future<T> spawn<T>(
+    String debugName,
+    FutureOr<T> Function() task, {
+    void Function()? preTask,
+    Duration? timeout, // per-job override
+  });
+
+  /// Currently running jobs.
+  List<WorkerInfo> getActiveWorkers();
+
+  /// All known jobs (active + completed + failed), up to a capped history.
+  List<WorkerInfo> getAllWorkers();
+
+  /// Optional: get a single worker by id.
+  WorkerInfo? getWorker(String id);
+
+  /// Remove completed/failed jobs older than [maxAge] from history.
+  void purge({Duration maxAge = const Duration(minutes: 30)});
+}
+
+enum WorkerStatus { running, completed, failed, timedOut }
+
+class WorkerInfo {
+  WorkerInfo({
+    required this.id,
+    required this.name,
+    required this.startedAt,
+    required this.status,
+    this.endedAt,
+    this.error,
+    this.stackTrace,
+  });
+
+  final String id;
+  final String name;
+  final DateTime startedAt;
+  final WorkerStatus status;
+  final DateTime? endedAt;
+  final Object? error;
+  final StackTrace? stackTrace;
+
+  Duration get duration => ((endedAt ?? DateTime.now()).difference(startedAt));
+}