Initial LibGDX project scaffold for ArtLegend

Multi-module Gradle setup targeting Android (S-Pen) and Desktop (Wacom/LWJGL3).
Includes core game stub, Android launcher with immersive mode, and desktop launcher.
Asset directory shared across platforms. Gradle 8.6, Kotlin 1.9.23, LibGDX 1.12.1.

build.gradle.kts

@@ -0,0 +1,21 @@
+buildscript {
+    val kotlinVersion: String by project
+    val androidGradleVersion: String by project
+
+    repositories {
+        mavenCentral()
+        google()
+    }
+
+    dependencies {
+        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion")
+        classpath("com.android.tools.build:gradle:$androidGradleVersion")
+    }
+}
+
+allprojects {
+    repositories {
+        mavenCentral()
+        google()
+    }
+}