- Introduced a `billable_filter` query parameter to filter tasks based on their billable status (billable, non-billable, or all).
- Updated the project finance controller to construct SQL queries with billable conditions based on the filter.
- Enhanced the frontend components to support billable filtering in project finance views and exports.
- Added corresponding translations for filter options in multiple languages.
- Refactored related API services to accommodate the new filtering logic.
- Introduced new appearance settings page with a dark mode toggle feature.
- Added localization support for English, Spanish, and Portuguese in appearance settings.
- Removed the ThemeSelector component and updated PreferenceSelector accordingly.
