Use idle and windows API to replace content script functionallity

[FelixSiegel]

The WebExtension API provides the idle and windows APIs, which offer information about the user's idle status, such as focus changes in a browser window. The idle state can be active, idle, or locked. For window focus, the onFocusedChanged event is triggered when a window's focus state changes.

Using these APIs eliminates the need for a content script that is injected into all web pages and relies on a "trick" to detect the absent status. This change will significantly improve performance and simplify the code.

For more information, see the following documentation:

• idle - Mozilla | MDN
• windows - Mozilla | MDN