Scaffold Java 21 multi-module project with UMD ISO + SFO parsing

- Gradle Kotlin DSL multi-module (core, ui, cli) with JPMS modules
- UMD ISO 9660 reader (UmdIsoReader/UmdIsoFile + sector devices)
- SFO (param.sfo) parser
- 'dump' CLI command: metadata + recursive file listing
- JUnit 5 + AssertJ tests (SFO and ISO reader)
- Switch license from MIT to GPL-3.0-or-later

core/build.gradle.kts

@@ -0,0 +1,20 @@
+plugins {
+    `java-library`
+}
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+dependencies {
+    testImplementation(platform(libs.junit.bom))
+    testImplementation(libs.junit.jupiter)
+    testRuntimeOnly(libs.junit.platform.launcher)
+    testImplementation(libs.assertj.core)
+}
+
+tasks.test {
+    useJUnitPlatform()
+}