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

.gitignore

@@ -0,0 +1,17 @@
+# Gradle
+.gradle/
+build/
+!gradle/wrapper/gradle-wrapper.jar
+
+# IDE
+.idea/
+*.iml
+.vscode/
+out/
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Disc images
+*.iso