Refactor: Move background image to main App composable and cleanup

This commit refactors the placement of the background image, moving it from `QuizScreen` to the main `KahootQuizApp` composable. This ensures the background is consistently applied across the app.

Additionally, this commit includes:
- Removal of unused Detekt configuration file (`ui/quiz/config/detekt/detekt.yml`).
- Minor code cleanup:
    - Removed commented-out code in `Theme.kt` and `Type.kt`.
    - Removed trailing blank lines in various domain model files.
    - Added `@file:Suppress("TooManyFunctions")` to `QuizMapper.kt`.
    - Added `@file:Suppress("MatchingDeclarationName")` to `QuizNavigation.kt`.
    - Used `1.seconds` instead of `1000` (Long) for delay in `QuizScreenViewModel`.

app/src/test/java/dev/adriankuta/kahootquiz/ExampleUnitTest.kt

@@ -13,4 +13,4 @@ class ExampleUnitTest {
     fun addition_isCorrect() {
         assertEquals(4, 2 + 2)
     }
-}
+}