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/pubspec.yaml

@@ -0,0 +1,22 @@
+name: flutter_melos_modular_scaffold
+publish_to: 'none'
+description: "A sample project using melos and modular scaffold."
+environment:
+  sdk: '>=3.10.0 <4.0.0'
+workspace:
+  - packages/design_system
+  - packages/core
+  - packages/domain
+  - packages/data_connect
+  - packages/core_localization
+  - packages/features/staff/authentication
+  - packages/features/client/authentication
+  - packages/features/client/home
+  - packages/features/client/settings
+  - packages/features/client/hubs
+  - apps/staff
+  - apps/client
+  - apps/design_system_viewer
+
+dev_dependencies:
+  melos: ^7.3.0