feat: enhance CPU details and improve UI/UX

This commit introduces several significant enhancements to both the backend data collection and the frontend presentation.

- Implements the display of full CPU flags:
  - The backend now parses the complete flags string from /proc/cpuinfo, providing more detailed hardware information.
  - The `CPUInfo` data model is updated with a `Flags` field to transport this data.
  - A collapsible "Flags" section is added to the CPU details card on the frontend, allowing users to view the extensive list without cluttering the main UI.

- Improves header design and functionality:
  - A GitHub icon linking to the source repository is added to the header.
  - The header layout is refactored using Flexbox for better alignment and a cleaner look.
  - A bottom border is added to the header for clear visual separation from the main dashboard content.
  - Responsiveness is improved, ensuring the header adapts gracefully to mobile viewports.

Author: ReturnFI