Fix js-dos ZIP extraction: add explicit directory entries to bundles

js-dos uses Emscripten's virtual filesystem which requires explicit
ZIP directory entries (names ending with '/') to create directories.
Java's ZipOutputStream only writes file entries, so subdirectories
like NAS50TH/TRACKS/WILKES/ were never created — causing Emscripten
'No such file or directory' errors for any path inside them.

- createBundle: before writing each file entry, add its parent
  directory as an explicit ZIP entry if not already added
- Affects all games with subdirectory structures (NASCAR Racing 2,
  Gus Goes to Cyberopolis, etc.)
- Use a HashSet to track already-added directories (no duplicates)

src/main/java/com/dostalgia/UploadResource.java

@@ -289,9 +289,20 @@ public class UploadResource {
 
         // ZIP it up directly from extractDir (no temp copy)
         try (var zos = new java.util.zip.ZipOutputStream(Files.newOutputStream(bundlePath))) {
+            var addedDirs = new java.util.HashSet<String>();
             Files.walk(extractDir).filter(Files::isRegularFile).forEach(f -> {
                 try {
                     String entryName = extractDir.relativize(f).toString().replace('\\', '/');
+                    // Ensure all parent directories have explicit entries
+                    // (js-dos Emscripten FS requires explicit directory entries)
+                    int idx = entryName.lastIndexOf('/');
+                    if (idx >= 0) {
+                        String parent = entryName.substring(0, idx + 1);
+                        if (addedDirs.add(parent)) {
+                            zos.putNextEntry(new java.util.zip.ZipEntry(parent));
+                            zos.closeEntry();
+                        }
+                    }
                     zos.putNextEntry(new java.util.zip.ZipEntry(entryName));
                     Files.copy(f, zos);
                     zos.closeEntry();