Add a small donation reminder on first install/update.

Minor compatibility improvements

Fixes for incognito mode (disabling it in firefox, using incognito:split in chrome).

Complete rewrite - it now makes API calls instead of inspecting the UI for changes.

This means more types of content are supported (the actual length of user preferences, for one, and any number of project knowledge files as well as the project's custom instructions) and it also supports different features being enabled across different chats automatically, without needing the checkbox menu.

Ensures the sidebar closes after processing the files. Before, the sidebar remained open until the AI was finished sending the response, which meant it would block the view entirely on mobile.