Move apps to mobile directory structure

Relocated all app directories (client, design_system_viewer, staff) and their contents under the new 'apps/mobile' path. This change improves project organization and prepares for future platform-specific structuring.

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

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+import 'package:equatable/equatable.dart';
+
+/// The workflow status of an [Invoice].
+enum InvoiceStatus {
+  /// Generated but not yet sent/finalized.
+  open,
+
+  /// Client has disputed a line item.
+  disputed,
+
+  /// Dispute has been handled.
+  resolved,
+
+  /// Invoice accepted by client.
+  verified,
+
+  /// Payment received.
+  paid,
+
+  /// Payment reconciled in accounting.
+  reconciled,
+
+  /// Payment not received by due date.
+  overdue,
+}
+
+/// Represents a bill sent to a [Business] for services rendered.
+class Invoice extends Equatable {
+  /// Unique identifier.
+  final String id;
+
+  /// The [Event] this invoice covers.
+  final String eventId;
+
+  /// The [Business] being billed.
+  final String businessId;
+
+  /// Current payment/approval status.
+  final InvoiceStatus status;
+
+  /// Grand total amount.
+  final double totalAmount;
+
+  /// Total amount for labor costs.
+  final double workAmount;
+
+  /// Total amount for addons/extras.
+  final double addonsAmount;
+
+  const Invoice({
+    required this.id,
+    required this.eventId,
+    required this.businessId,
+    required this.status,
+    required this.totalAmount,
+    required this.workAmount,
+    required this.addonsAmount,
+  });
+
+  @override
+  List<Object?> get props => [
+        id,
+        eventId,
+        businessId,
+        status,
+        totalAmount,
+        workAmount,
+        addonsAmount,
+      ];
+}

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

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+import 'package:equatable/equatable.dart';
+
+/// Represents a reason or log for a declined [Invoice].
+class InvoiceDecline extends Equatable {
+  /// Unique identifier.
+  final String id;
+
+  /// The [Invoice] that was declined.
+  final String invoiceId;
+
+  /// Reason provided by the client.
+  final String reason;
+
+  /// When the decline happened.
+  final DateTime declinedAt;
+
+  const InvoiceDecline({
+    required this.id,
+    required this.invoiceId,
+    required this.reason,
+    required this.declinedAt,
+  });
+
+  @override
+  List<Object?> get props => [id, invoiceId, reason, declinedAt];
+}

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

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+import 'package:equatable/equatable.dart';
+
+/// Represents a line item in an [Invoice].
+///
+/// Corresponds to the work done by one [Staff] member.
+class InvoiceItem extends Equatable {
+  /// Unique identifier.
+  final String id;
+
+  /// The [Invoice] this item belongs to.
+  final String invoiceId;
+
+  /// The [Staff] member whose work is being billed.
+  final String staffId;
+
+  /// Total billed hours.
+  final double workHours;
+
+  /// Hourly rate applied.
+  final double rate;
+
+  /// Total line item amount (workHours * rate).
+  final double amount;
+
+  const InvoiceItem({
+    required this.id,
+    required this.invoiceId,
+    required this.staffId,
+    required this.workHours,
+    required this.rate,
+    required this.amount,
+  });
+
+  @override
+  List<Object?> get props => [id, invoiceId, staffId, workHours, rate, amount];
+}

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

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+import 'package:equatable/equatable.dart';
+
+/// Status of a staff payout.
+enum PaymentStatus {
+  /// Payout calculated but not processed.
+  pending,
+
+  /// Submitted to banking provider.
+  processing,
+
+  /// Successfully transferred to staff.
+  paid,
+
+  /// Transfer failed.
+  failed,
+}
+
+/// Represents a payout to a [Staff] member for a completed [Assignment].
+class StaffPayment extends Equatable {
+  /// Unique identifier.
+  final String id;
+
+  /// The recipient [Staff].
+  final String staffId;
+
+  /// The [Assignment] being paid for.
+  final String assignmentId;
+
+  /// Amount to be paid.
+  final double amount;
+
+  /// Processing status.
+  final PaymentStatus status;
+
+  /// When the payment was successfully processed.
+  final DateTime? paidAt;
+
+  const StaffPayment({
+    required this.id,
+    required this.staffId,
+    required this.assignmentId,
+    required this.amount,
+    required this.status,
+    this.paidAt,
+  });
+
+  @override
+  List<Object?> get props => [id, staffId, assignmentId, amount, status, paidAt];
+}