feat(io): OggMusicBackend + SwingIO wiring; music/ folder + docs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Semesterprojekt/pom.xml

@@ -49,6 +49,18 @@
             <version>${logback.version}</version>
         </dependency>
 
+        <!-- OGG Vorbis decoding (GUI background music) -->
+        <dependency>
+            <groupId>com.googlecode.soundlibs</groupId>
+            <artifactId>vorbisspi</artifactId>
+            <version>1.0.3.3</version>
+        </dependency>
+        <dependency>
+            <groupId>com.googlecode.soundlibs</groupId>
+            <artifactId>jorbis</artifactId>
+            <version>0.0.17.4</version>
+        </dependency>
+
         <!-- Tests -->
         <dependency>
             <groupId>org.junit.jupiter</groupId>