feat(io): GameIO music seams; push room track per turn, silence at menu

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

Semesterprojekt/src/test/java/thb/jeanluc/adventure/io/MusicSeamDefaultTest.java

@@ -0,0 +1,17 @@
+package thb.jeanluc.adventure.io;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class MusicSeamDefaultTest {
+
+    @Test
+    void defaultMusicSeamsAreSilentNoOps() {
+        TestIO io = new TestIO();
+        io.setMusic("anything.ogg");
+        io.setMusic(null);
+        io.setMusicLevel(MusicLevel.HIGH);
+        assertThat(io.outputs()).isEmpty();
+    }
+}