feat: added dark theme to example

[alduzy]

Description

This PR adds dark theme to the example app. The theme changes automatically based on the device's appearance setting and can be changed by clicking a button.

Changes

• added dark styles to screens and components
• added a state and listener for basic theme management
• added a dark mode button

Screenshots / GIFs

Screen.Recording.2024-07-09.at.17.01.37.mov

Screen.Recording.2024-07-09.at.17.55.02.mov

Test code and steps to reproduce

• Use the Example app
• Toggle the theme with a button or by changing device's setting
• Browse screens

Checklist

• Included code example that can be used to test this change
• Ensured that CI passes

[kkafar]

The code looks solid. I haven't played out around with the app itself yet.

My only suggestion for now, seeing the repetition in the Text / View components would be to create some wrappers such as ThemedText / ThemedView that would use value from context and adjust the style internally. Using HOC is also reasonable here. This way we could avoid much of the repetition.

[kkafar]

Looks solid 💪🏻