Implement Native Dark Mode with Customization Options

Is your feature request related to a problem? Please describe.
Currently, Refly does not have a native dark mode. Users who prefer dark themes often rely on browser extensions like Dark Reader. While these extensions provide a dark theme, the automatically generated color palettes can sometimes look inconsistent or less aesthetically pleasing compared to a theme specifically designed for the application. Additionally, these extensions might not offer the same level of customization as a native implementation.

Describe the solution you'd like
I propose adding native dark mode support to the Refly project. This would allow users to switch to a dark theme directly within the application settings.

Describe the alternative solutions you've considered
Using browser extensions like Dark Reader is a current workaround. However, as mentioned, the color schemes generated by such tools are often not optimized and can look jarring (as observed with Dark Reader on Refly, the overall look isn't very coordinated). A native implementation allows for a curated design.

Describe the features you'd like to see included in the dark mode:

1. Aesthetic Color Palette: The dark mode should feature a carefully designed and aesthetically pleasing color scheme. The colors should be chosen to ensure good contrast, readability, and overall visual harmony, specifically tailored for Refly's interface, rather than relying on automatic color inversion. The goal is a visually comfortable and appealing dark theme.
2. Custom Font Option: Similar to features found in some dark mode tools (like Dark Reader), it would be highly beneficial to include an option for users to select or specify a custom font to be used when the dark theme is active. This allows for greater personalization and can improve readability for different users based on their preferences.

Additional context
Implementing a native dark mode would greatly enhance the user experience, reduce eye strain for users who prefer darker interfaces, and make Refly more accessible and visually appealing across different lighting conditions.

Thank you for considering this feature request!