docs: 更新协议文档，删除废弃计划文档

- 更新 http-error-codes, user-points-chat-data-protocol
- 更新 divination-run-protocol, profile-protocol
- 删除废弃的后端和前端设计计划文档

apps/lib/features/divination/data/models/follow_up_message.dart

@@ -0,0 +1,52 @@
+class FollowUpMessage {
+  const FollowUpMessage({
+    required this.id,
+    required this.seq,
+    required this.role,
+    required this.content,
+    required this.timestamp,
+  });
+
+  final String id;
+  final int seq;
+  final String role;
+  final String content;
+  final DateTime timestamp;
+
+  factory FollowUpMessage.fromJson(Map<String, dynamic> json) {
+    return FollowUpMessage(
+      id: _requiredString(json, 'id'),
+      seq: _requiredInt(json, 'seq'),
+      role: _requiredString(json, 'role'),
+      content: _requiredStringAllowEmpty(json, 'content'),
+      timestamp: DateTime.parse(_requiredString(json, 'timestamp')).toLocal(),
+    );
+  }
+}
+
+String _requiredString(Map<String, dynamic> json, String key) {
+  final value = json[key];
+  if (value is! String || value.isEmpty) {
+    throw FormatException('Missing required string: $key');
+  }
+  return value;
+}
+
+String _requiredStringAllowEmpty(Map<String, dynamic> json, String key) {
+  final value = json[key];
+  if (value is! String) {
+    throw FormatException('Missing required string: $key');
+  }
+  return value;
+}
+
+int _requiredInt(Map<String, dynamic> json, String key) {
+  final value = json[key];
+  if (value is int) {
+    return value;
+  }
+  if (value is num) {
+    return value.toInt();
+  }
+  throw FormatException('Missing required int: $key');
+}