feat: Add skeleton loading UI components for various screens

- Implemented `Skeleton.kt` for loading placeholders in the app, including lesson cards, schedule, overview, and subjects.
- Introduced `Undo.kt` to manage undo actions with a snackbar interface.
- Created `WeekWidget.kt` for a widget displaying the week's schedule, including dynamic updates based on the current timetable.
- Added various splash animations in the `animator` directory for a smooth launch experience.
- Designed drawable resources for the widget and splash screen, including icons for city and room moves.
- Defined XML resources for widget configuration and photo paths.

android/app/build.gradle.kts

@@ -59,6 +59,7 @@ dependencies {
     implementation(libs.lifecycle.viewmodel.compose)
     implementation(libs.lifecycle.runtime.compose)
     implementation(libs.core.ktx)
+    implementation(libs.splashscreen)
     implementation(libs.coroutines.android)
     implementation(libs.serialization.json)
     implementation(libs.okhttp)