fix: resolveSibling using filename only, not full bundle path

bundleFile changed from 'wolf3d.jsdos' to 'wolf3d/wolf3d.jsdos' when
bundles moved inside game directories. resolveSibling(bundleFile + '.tmp')
produced a wrong nested path. Now uses bundlePath.getFileName() to get
just the filename part before appending .tmp.

src/main/java/com/dostalgia/GameService.java

@@ -171,7 +171,7 @@ public class GameService {
         byte[] newJsdosJson = buildJsdosJsonBytes(executable);
 
         // Patch the ZIP: read old, write new with modified config entries
-        Path tmpPath = bundlePath.resolveSibling(bundleFile + ".tmp");
+        Path tmpPath = bundlePath.resolveSibling(bundlePath.getFileName() + ".tmp");
         try (var zis = new java.util.zip.ZipInputStream(Files.newInputStream(bundlePath));
              var zos = new java.util.zip.ZipOutputStream(Files.newOutputStream(tmpPath))) {