Fix lint issues in MainActivity.kt

[JesseScott]

This PR addresses two specific lint issues identified in MainActivity.kt:

1. It removes an unused import that was cluttering the file.
2. It migrates from the legacy values() method on the Screens enum to the newer entries property introduced in Kotlin 1.9.0. This optimization avoids array allocation on every access, which is the recommended approach for performance and readability.

Fixes #93

---

PR created automatically by Jules for task 15934058740003085136 started by @JesseScott

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.