feat: Enhance QuizScreen UI and introduce core design system module

This commit significantly revamps the `QuizScreen` UI to display question details including image and text, and introduces a new `core:designsystem` module to centralize theme, colors, typography, and drawable resources.

Key changes:

- **UI Layer (`ui:quiz` module):**
    - Updated `QuizScreen.kt`:
        - Implemented a background image for the screen.
        - Added a `Toolbar` composable to display question progress and type.
        - Created `QuestionContent` composable to show the question image (using Coil for image loading) and text.
        - Added a placeholder `Choices` composable (currently an empty `LazyVerticalGrid`).
        - Applied `fillMaxSize()` to the main `QuizScreen` modifier.
        - Included a `@Preview` for `QuizScreen` with sample data.
    - Modified `QuizScreenViewModel.kt` to update `QuizUiState` with the first `Question` from the fetched quiz.
    - Added a `quiz` string resource in `strings.xml`.
    - Added dependencies for Coil (compose and okhttp) in `ui/quiz/build.gradle.kts`.
- **Core Design System (`core:designsystem` module):**
    - Created a new Android library module `core:designsystem`.
    - Moved `Color.kt`, `Theme.kt`, and `Type.kt` from `app/src/main/java/dev/adriankuta/kahootquiz/ui/theme` to this new module.
    - Added a new `Grey` color to `Color.kt`.
    - Added `bg_image.webp` and `ic_type.xml` drawable resources.
    - Configured the module with `kahootquiz.android.library.compose` plugin.
- **App Module (`app` module):**
    - Updated `MainActivity.kt` to import `KahootQuizTheme` from the new `core.designsystem` package.
    - Added `implementation(projects.core.designsystem)` dependency in `app/build.gradle.kts`.
- **Domain Layer (`domain` module):**
    - Made several fields in `Question.kt` and `Choice.kt` nullable and provided default null values to accommodate potential missing data from the API.
    - Specifically, `Question.image` is now non-nullable (`String`).
- **Build System:**
    - Added `coilCompose` and `coilNetworkOkhttp` versions to `gradle/libs.versions.toml`.
    - Included `:core:designsystem` in `settings.gradle.kts`.

domain/src/main/kotlin/dev/adriankuta/kahootquiz/domain/models/Choice.kt

@@ -3,5 +3,5 @@ package dev.adriankuta.kahootquiz.domain.models
 data class Choice(
     val answer: String?,
     val correct: Boolean?,
-    val languageInfo: LanguageInfo?
+    val languageInfo: LanguageInfo? = null
 )

domain/src/main/kotlin/dev/adriankuta/kahootquiz/domain/models/Question.kt

@@ -8,16 +8,16 @@ data class Question(
     val type: String?,
     val question: String?,
     val time: Duration?,
-    val points: Boolean?,
+    val points: Boolean? = null,
     val pointsMultiplier: Int?,
     val choices: List<Choice>?,
-    val layout: String?,
-    val image: String?,
+    val layout: String? = null,
+    val image: String,
     val imageMetadata: ImageMetadata?,
-    val resources: String?,
-    val video: Video?,
-    val questionFormat: Int?,
-    val languageInfo: LanguageInfo?,
-    val media: List<MediaItem>?,
-    val choiceRange: ChoiceRange?
+    val resources: String? = null,
+    val video: Video? = null,
+    val questionFormat: Int? = null,
+    val languageInfo: LanguageInfo? = null,
+    val media: List<MediaItem>? = null,
+    val choiceRange: ChoiceRange? = null
 )