feat: Refactor bank account handling in billing and staff modules

- Introduced new bank account entities: BusinessBankAccount and StaffBankAccount.
- Updated bank account adapter to handle new entities.
- Removed legacy BankAccount entity and its adapter.
- Implemented use case for fetching bank accounts in billing repository.
- Updated BillingBloc and BillingState to include bank accounts.
- Refactored PaymentMethodCard to display bank account information.
- Adjusted actions widget layout for better UI consistency.
- Updated staff bank account repository and use cases to utilize new entity structure.
- Ensured all references to bank accounts in the codebase are updated to the new structure.

apps/mobile/packages/domain/lib/src/entities/financial/bank_account/bank_account.dart

@@ -0,0 +1,27 @@
+import 'package:equatable/equatable.dart';
+
+/// Abstract base class for all types of bank accounts.
+abstract class BankAccount extends Equatable {
+  /// Creates a [BankAccount].
+  const BankAccount({
+    required this.id,
+    required this.bankName,
+    required this.isPrimary,
+    this.last4,
+  });
+
+  /// Unique identifier.
+  final String id;
+
+  /// Name of the bank or provider.
+  final String bankName;
+
+  /// Whether this is the primary payment method.
+  final bool isPrimary;
+
+  /// Last 4 digits of the account/card.
+  final String? last4;
+
+  @override
+  List<Object?> get props => <Object?>[id, bankName, isPrimary, last4];
+}

apps/mobile/packages/domain/lib/src/entities/financial/bank_account/business_bank_account.dart

@@ -0,0 +1,26 @@
+import 'bank_account.dart';
+
+/// Domain model representing a business bank account or payment method.
+class BusinessBankAccount extends BankAccount {
+  /// Creates a [BusinessBankAccount].
+  const BusinessBankAccount({
+    required super.id,
+    required super.bankName,
+    required String last4,
+    required super.isPrimary,
+    this.expiryTime,
+  }) : super(last4: last4);
+
+  /// Expiration date if applicable.
+  final DateTime? expiryTime;
+
+  @override
+  List<Object?> get props => <Object?>[
+    ...super.props,
+    expiryTime,
+  ];
+
+  /// Getter for non-nullable last4 in Business context.
+  @override
+  String get last4 => super.last4!;
+}

apps/mobile/packages/domain/lib/src/entities/financial/bank_account/staff_bank_account.dart

@@ -0,0 +1,48 @@
+import 'bank_account.dart';
+
+/// Type of staff bank account.
+enum StaffBankAccountType {
+  /// Checking account.
+  checking,
+
+  /// Savings account.
+  savings,
+
+  /// Other type.
+  other,
+}
+
+/// Domain entity representing a staff's bank account.
+class StaffBankAccount extends BankAccount {
+  /// Creates a [StaffBankAccount].
+  const StaffBankAccount({
+    required super.id,
+    required this.userId,
+    required super.bankName,
+    required this.accountNumber,
+    required this.accountName,
+    required super.isPrimary,
+    super.last4,
+    this.sortCode,
+    this.type = StaffBankAccountType.checking,
+  });
+
+  /// User identifier.
+  final String userId;
+
+  /// Full account number.
+  final String accountNumber;
+
+  /// Name of the account holder.
+  final String accountName;
+
+  /// Sort code (optional).
+  final String? sortCode;
+
+  /// Account type.
+  final StaffBankAccountType type;
+
+  @override
+  List<Object?> get props =>
+      <Object?>[...super.props, userId, accountNumber, accountName, sortCode, type];
+}