feat(headline): create headline state

- Added CreateHeadlineStatus enum
- Implemented CreateHeadlineState class
- Added form validation logic

Author: fulleni

lib/content_management/bloc/create_headline/create_headline_state.dart

@@ -0,0 +1,90 @@
+part of 'create_headline_bloc.dart';
+
+/// Represents the status of the create headline operation.
+enum CreateHeadlineStatus {
+  /// Initial state, before any data is loaded.
+  initial,
+
+  /// Data is being loaded.
+  loading,
+
+  /// An operation completed successfully.
+  success,
+
+  /// An error occurred.
+  failure,
+
+  /// The form is being submitted.
+  submitting,
+}
+
+/// The state for the [CreateHeadlineBloc].
+final class CreateHeadlineState extends Equatable {
+  const CreateHeadlineState({
+    this.status = CreateHeadlineStatus.initial,
+    this.title = '',
+    this.description = '',
+    this.url = '',
+    this.imageUrl = '',
+    this.source,
+    this.category,
+    this.sources = const [],
+    this.categories = const [],
+    this.errorMessage,
+  });
+
+  final CreateHeadlineStatus status;
+  final String title;
+  final String description;
+  final String url;
+  final String imageUrl;
+  final Source? source;
+  final Category? category;
+  final List<Source> sources;
+  final List<Category> categories;
+  final String? errorMessage;
+
+  /// Returns true if the form is valid and can be submitted.
+  bool get isFormValid => title.isNotEmpty;
+
+  CreateHeadlineState copyWith({
+    CreateHeadlineStatus? status,
+    String? title,
+    String? description,
+    String? url,
+    String? imageUrl,
+    ValueGetter<Source?>? source,
+    ValueGetter<Category?>? category,
+    List<Source>? sources,
+    List<Category>? categories,
+    String? errorMessage,
+  }) {
+    return CreateHeadlineState(
+      status: status ?? this.status,
+      title: title ?? this.title,
+      description: description ?? this.description,
+      url: url ?? this.url,
+      imageUrl: imageUrl ?? this.imageUrl,
+      source: source != null ? source() : this.source,
+      category: category != null ? category() : this.category,
+      sources: sources ?? this.sources,
+      categories: categories ?? this.categories,
+      errorMessage: errorMessage ?? this.errorMessage,
+    );
+  }
+
+  @override
+  List<Object?> get props => [
+        status,
+        title,
+        description,
+        url,
+        imageUrl,
+        source,
+        category,
+        sources,
+        categories,
+        errorMessage,
+      ];
+}
+