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/.gitignore

@@ -0,0 +1,22 @@
+# Old apps prototypes
+prototypes/*
+
+# AI prompts
+ai_prompts/*
+
+# Docs
+docs/*
+
+# Template feature
+packages/features/shared/template_feature/*
+
+# Generated files
+*.g.dart
+*.freezed.dart
+
+# Dart/Flutter
+.dart_tool/
+.packages
+.pub-cache/
+.pub/
+build/