refactor: move MainActivity (#1417)

Description

Move MainActivity to ui package.

Screenshots

Technical details

Tests

1. Play store deep links - ✅
2. Self update through Gitlab releases - ✅
3. Icon on launcher doesn't shift - ✅

Issues

https://gitlab.e.foundation/e/os/backlog/-/issues/1417

10 commandments of code reviews

👪 ❤ https://gitlab.e.foundation/internal/wiki/-/wikis/mobile-team/guidelines/Code-review

Summary by CodeRabbit

• New Features

  • Restructured package organization by moving MainActivity to a dedicated ui subpackage, enhancing code clarity.

• Bug Fixes

  • Updated references to MainActivity across various files to reflect the new package structure, ensuring proper functionality.

• Documentation

  • Improved organization of UI-related components, which may aid developers in navigating the codebase more effectively.