Migrate to ThemeProvider for Styling

[livoszlak]

Refactor the project to use a ThemeProvider for managing styles and themes. This will centralize the styling logic and make it easier to switch between themes (e.g., light and dark mode). Note: colors for dark as well as light mode are not set - feel free to suggest good combinations of colors!

The following tasks should be completed:

• 1. Install necessary dependencies for theming (@mui/material's ThemeProvider).
• 2. Create a theme configuration file (src/theme.js) to define the theme settings for both lightTheme and darkTheme.
• 3. Wrap the root component in src/main.jsx with the ThemeProvider.
• 4. Update all components to use theme values instead of hardcoded styles.
• 5. Remove inline styles and migrate them to the theme configuration where applicable.
• 6. Ensure that the ThemeProvider supports both light and dark modes, and add a toggle mechanism in the UI; perhaps a MUI switch would work well for this.