Initial scaffold: FocusFlow shared Dart package

Models (Task, Streak, StreakEntry, Reward, User, TimeEstimate, CoworkingRoom, ApiResponse),
enums (EnergyLevel, TaskStatus, RewardType, RewardStyle),
constants (ApiConstants, ErrorCodes, AppLimits), validators, and generated .g.dart files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/src/models/task.dart

@@ -0,0 +1,56 @@
+import 'package:json_annotation/json_annotation.dart';
+part 'task.g.dart';
+
+@JsonSerializable()
+class Task {
+  final String id;
+  final String userId;
+  final String title;
+  final String? description;
+  final String status; // pending, in_progress, completed, skipped, archived
+  final int priority; // 0-100, ML-adjusted
+  final String energyLevel; // low, medium, high
+  final int? estimatedMinutes;
+  final int? actualMinutes;
+  final DateTime? dueAt;
+  final DateTime? completedAt;
+  final String? parentTaskId;
+  final double? dopamineScore; // ML-computed 0-100
+  final double noveltyFactor; // decays over time
+  final DateTime? lastInteracted;
+  final int timesPostponed;
+  final List<String> tags;
+  final String? category;
+  final String? color;
+  final int version;
+  final DateTime createdAt;
+  final DateTime? updatedAt;
+
+  const Task({
+    required this.id,
+    required this.userId,
+    required this.title,
+    this.description,
+    this.status = 'pending',
+    this.priority = 0,
+    this.energyLevel = 'medium',
+    this.estimatedMinutes,
+    this.actualMinutes,
+    this.dueAt,
+    this.completedAt,
+    this.parentTaskId,
+    this.dopamineScore,
+    this.noveltyFactor = 1.0,
+    this.lastInteracted,
+    this.timesPostponed = 0,
+    this.tags = const [],
+    this.category,
+    this.color,
+    this.version = 1,
+    required this.createdAt,
+    this.updatedAt,
+  });
+
+  factory Task.fromJson(Map<String, dynamic> json) => _$TaskFromJson(json);
+  Map<String, dynamic> toJson() => _$TaskToJson(this);
+}