perf: improve ui (#7178)

* perf: enhance layout responsiveness and text handling in stats page

* perf: enhance subagent, future task UI

- Updated the overall structure of the SubAgentPage component for better readability and maintainability.
- Introduced a new dashboard layout with improved header and action buttons.
- Replaced the old settings card with a more visually appealing setting card design.
- Enhanced the agent list section with a more user-friendly display and added empty state handling.
- Implemented unsaved changes notification and confirmation dialogs for better user interaction.
- Refactored code for better clarity and organization, including the use of computed properties for state management.