feat(create-source): add state for create source bloc

- Defines CreateSourceStatus enum
- Implements CreateSourceState class
- Adds state properties and copyWith method
- Includes basic form validation
- Uses Equatable for state comparison

Author: fulleni

lib/content_management/bloc/create_source/create_source_state.dart

@@ -0,0 +1,85 @@
+part of 'create_source_bloc.dart';
+
+/// Represents the status of the create source operation.
+enum CreateSourceStatus {
+  /// 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 [CreateSourceBloc].
+final class CreateSourceState extends Equatable {
+  /// {@macro create_source_state}
+  const CreateSourceState({
+    this.status = CreateSourceStatus.initial,
+    this.name = '',
+    this.description = '',
+    this.url = '',
+    this.sourceType,
+    this.language = '',
+    this.headquarters,
+    this.countries = const [],
+    this.errorMessage,
+  });
+
+  final CreateSourceStatus status;
+  final String name;
+  final String description;
+  final String url;
+  final SourceType? sourceType;
+  final String language;
+  final Country? headquarters;
+  final List<Country> countries;
+  final String? errorMessage;
+
+  /// Returns true if the form is valid and can be submitted.
+  bool get isFormValid => name.isNotEmpty;
+
+  CreateSourceState copyWith({
+    CreateSourceStatus? status,
+    String? name,
+    String? description,
+    String? url,
+    ValueGetter<SourceType?>? sourceType,
+    String? language,
+    ValueGetter<Country?>? headquarters,
+    List<Country>? countries,
+    String? errorMessage,
+  }) {
+    return CreateSourceState(
+      status: status ?? this.status,
+      name: name ?? this.name,
+      description: description ?? this.description,
+      url: url ?? this.url,
+      sourceType: sourceType != null ? sourceType() : this.sourceType,
+      language: language ?? this.language,
+      headquarters: headquarters != null ? headquarters() : this.headquarters,
+      countries: countries ?? this.countries,
+      errorMessage: errorMessage,
+    );
+  }
+
+  @override
+  List<Object?> get props => [
+    status,
+    name,
+    description,
+    url,
+    sourceType,
+    language,
+    headquarters,
+    countries,
+    errorMessage,
+  ];
+}