Refactor: use 'app' instead of 'application'

Updated terminology in README and app.js to use 'app' instead of 'application' for consistency and brevity across documentation and code comments.

README.md

@@ -123,7 +123,7 @@ The META.js Customizer follows a modern, modular architecture designed for maint
 
 #### **🎯 MetaJSCustomizer (Main Controller)**
 
-- Application lifecycle management and component orchestration
+- App lifecycle management and component orchestration
 - Global error handling with user-friendly feedback
 - Performance monitoring and optimization
 - Loading state management and initialization coordination