Refactor: Frontend UI consistency

[arabcoders]

This pull request introduces a range of frontend UI improvements and documentation updates. The frontend changes focus on standardizing card and panel component styles, refining border and background handling, and introducing new utility classes for consistent UI surfaces. In documentation, there are updates to API references and error code descriptions, including the removal of a deprecated endpoint and a more detailed system report example.

Frontend UI consistency and enhancements:

• Standardized the appearance of UCard components across several files by removing redundant border classes and relying on updated UI configuration and utility classes for borders and backgrounds.
• Updated Tailwind CSS variables and introduced new utility classes for borders, cards, panels, floating surfaces, and page headers to ensure a consistent look and feel, including improved support for dark mode.
• Improved transition effects for page navigation for a smoother user experience.

Component and UX tweaks:

• Adjusted the order and structure of confirm/cancel buttons in the Dialog component for better usability.
• Updated the background color of duplicate record list items for better visual distinction.

Documentation updates:

• Removed the deprecated POST /v1/api/backends/validate/token/{type} endpoint from the API documentation. (API.md) [1] [2]
• Updated the system report API documentation to show a detailed, structured example response. (API.md)
• Clarified and renamed error code DM001 in the FAQ for better error traceability. (FAQ.md)