Web based interface for generating the dynamic links

### Is your feature request related to a problem? Please describe.

I would like to propose a feature addition to the project: a web-based interface for generating GitHub README stats dynamically.

Currently, users must manually construct URLs with query parameters such as username and theme. While functional, this can be confusing for beginners and prone to formatting errors. The proposed feature would provide a simple UI where users can:

* Enter their GitHub username
* Select a theme from a dropdown
* Toggle optional parameters (e.g., show_icons, hide_border, etc.)
* Instantly preview the generated card
* Copy the ready-to-use Markdown snippet

Implementation details:

* Add a static `index.html` interface (placed in root or public folder).
* Use Vercel rewrites to serve the interface at `/`.
* No changes to existing API routes.
* Fully backward compatible and optional for users.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_