feat(io): bundle background music as classpath resources

Switch OggMusicBackend from streaming an external, git-ignored music/ folder
(relative to the run directory) to streaming bundled classpath resources under
/music/, so the four manor tracks ship inside the JAR and play out of the box —
consistent with how fonts are bundled. The play loop reopens the resource each
iteration via a BufferedInputStream (the vorbisspi SPI needs mark/reset to read
the OGG header). Missing tracks still fall back to silence.

Add the four converted OGG Vorbis tracks (manor-theme/cellar-drone/musicbox/
lament) under src/main/resources/music/, un-ignore that path, and re-anchor the
gitignore so only the top-level MP3 source folder stays ignored. Update
docs/music.md for the bundled approach and conversion recipes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Semesterprojekt/src/main/java/thb/jeanluc/adventure/io/OggMusicBackend.java

@@ -7,20 +7,20 @@ import javax.sound.sampled.AudioInputStream;
 import javax.sound.sampled.AudioSystem;
 import javax.sound.sampled.FloatControl;
 import javax.sound.sampled.SourceDataLine;
-import java.nio.file.Files;
-import java.nio.file.Path;
+import java.io.BufferedInputStream;
+import java.io.InputStream;
 
 /**
- * Streams OGG Vorbis tracks from the external {@code music/} folder through a
- * {@link SourceDataLine}, looping, with ~400 ms gain fades. Decoding uses the
- * vorbisspi/jorbis {@code javax.sound} SPI. All playback runs on a daemon
- * thread; missing/undecodable files are logged and stay silent. GUI-only —
- * verified manually.
+ * Streams OGG Vorbis tracks bundled on the classpath under {@code /music/}
+ * through a {@link SourceDataLine}, looping, with ~400 ms gain fades. Decoding
+ * uses the vorbisspi/jorbis {@code javax.sound} SPI. All playback runs on a
+ * daemon thread; missing/undecodable files are logged and stay silent. GUI-only
+ * — verified manually.
  */
 @Slf4j
 public final class OggMusicBackend implements MusicBackend {
 
-    private static final String MUSIC_DIR = "music";
+    private static final String MUSIC_DIR = "/music/";
     private static final int FADE_MS = 400;
     private static final int FADE_STEPS = 20;
     private static final int BUFFER = 4096;
@@ -35,13 +35,13 @@ public final class OggMusicBackend implements MusicBackend {
     public synchronized void fadeTo(String track, float gainDb) {
         stopCurrent();
         targetGainDb = gainDb;
-        Path file = Path.of(MUSIC_DIR, track);
-        if (!Files.isReadable(file)) {
-            log.warn("Music file not found, staying silent: {}", file);
+        String resource = MUSIC_DIR + track;
+        if (getClass().getResource(resource) == null) {
+            log.warn("Music resource not found, staying silent: {}", resource);
             return;
         }
         stopping = false;
-        playThread = new Thread(() -> playLoop(file, gainDb), "music");
+        playThread = new Thread(() -> playLoop(resource, gainDb), "music");
         playThread.setDaemon(true);
         playThread.start();
     }
@@ -80,11 +80,14 @@ public final class OggMusicBackend implements MusicBackend {
         playThread = null;
     }
 
-    private void playLoop(Path file, float gainDb) {
+    private void playLoop(String resource, float gainDb) {
         SourceDataLine l = null;
         try {
             while (!stopping) {
-                try (AudioInputStream in = AudioSystem.getAudioInputStream(file.toFile())) {
+                // Reopen the bundled resource each loop; BufferedInputStream gives
+                // the SPI the mark/reset support it needs to read the OGG header.
+                try (InputStream res = getClass().getResourceAsStream(resource);
+                     AudioInputStream in = AudioSystem.getAudioInputStream(new BufferedInputStream(res))) {
                     AudioFormat base = in.getFormat();
                     AudioFormat pcm = new AudioFormat(AudioFormat.Encoding.PCM_SIGNED,
                             base.getSampleRate(), 16, base.getChannels(),
@@ -106,7 +109,7 @@ public final class OggMusicBackend implements MusicBackend {
                 }
             }
         } catch (Exception e) {
-            log.warn("Music playback failed for {}: {}", file, e.getMessage());
+            log.warn("Music playback failed for {}: {}", resource, e.getMessage());
         } finally {
             if (l != null) {
                 try {