fix(routes): show system routes table even if no custom routes are defined

[m-dilorenzi]

This pull request updates the RoutesContent.vue component to improve icon usage, loading state handling, and UI consistency. The changes primarily focus on showing the system routes table even if no custom routes are defined.

Tables

• removed && routes.length condition on the main <div> containing the two tables to allow the system routes table view even if no custom routes are defined.

Icon usage improvements:

• Replaced all string-based FontAwesome icon references (e.g., ['fas', 'circle-info']) with imported icon variables (e.g., faCircleInfo, faTable, faPenToSquare, etc.), ensuring more consistent and type-safe icon handling throughout the component.

Loading state and error handling:

• Added explicit loading.value = true and loading.value = false handling in the loadMainTable function to ensure the loading skeleton is displayed correctly during data fetching, and always hidden after completion or error.

UI and user experience enhancements:

• Updated the display logic for skeleton loaders and empty states, moving them outside the main table container for better visual structure and adding spacing classes for improved layout.
• Enhanced the visual feedback for route status icons by adding green/red color classes to the enabled/disabled icons, improving accessibility and clarity.

Closes: NethServer/nethsecurity#1447