refactor(web-ui): Apply modular structure and refactor dashboard

This commit applies the modular refactoring to the web-ui,
including the new daily attendance tracking feature.

- **Modular Structure:** Re-introduced the modular files 'config.js',
  'component-loader.js', and 'navigation.js' to centralize configuration,
  component loading, and navigation logic.
- **Refactored Dashboard:** Refactored 'group-leader-dashboard.js' to use
  the new 'apiCall' function from 'api-config.js' for API requests,
  removing duplicated code and improving error handling.
- **ES6 Modules:** Updated 'group-leader.html' to load scripts as
  ES6 modules ('type="module"'), ensuring compatibility with the
  modular JavaScript files.
- **Clean-up:** Removed unnecessary global variables and duplicated
  functions, improving code quality and maintainability.

web-ui/js/config.js

@@ -37,4 +37,4 @@ export const config = {
     // 토큰 만료 확인 주기 (밀리초 단위, 예: 5분)
     tokenRefreshInterval: 5 * 60 * 1000,
   }
-};
+};