BUG: Prevent image dragging on landing website

### Is there an existing issue for this?

- [x] I have searched the existing issues

### What happened?

### Description

Currently, images on the Pictopy landing page can be dragged by users, which affects the overall user experience and UI polish.

To improve UX and maintain a clean interaction on the landing page, image dragging should be disabled globally.

#### Screenshot :

### Proposed Solution

Disable image dragging using CSS.

### Implementation

Update index.css with the following rule:
```
/* Prevent image dragging */
img {
-webkit-user-drag: none;
-khtml-user-drag: none;
-moz-user-drag: none;
-o-user-drag: none;
user-drag: none;
}
```

Expected Result

- Images cannot be dragged on the landing page
- Cleaner and more controlled UI interaction
- Improved user experience

### Record

- [x] I agree to follow this project's Code of Conduct