Fix nested directory entries: add full ancestor chain to ZIP

Previously only the immediate parent directory was added as a ZIP
entry. For deeply nested paths like NAS50TH/TRACKS/WILKES/WILKES.DAT,
only NAS50TH/TRACKS/WILKES/ was created — but NAS50TH/TRACKS/ and
NAS50TH/ were skipped (they're only parents of other directories,
never the immediate parent of a file).

Emscripten's FS.createDirectory() fails if parent doesn't exist,
so intermediate directories must be in the ZIP too.

Now walks up the full ancestor chain with a while loop.

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

@@ -293,15 +293,16 @@ public class UploadResource {
             Files.walk(extractDir).filter(Files::isRegularFile).forEach(f -> {
                 try {
                     String entryName = extractDir.relativize(f).toString().replace('\\', '/');
-                    // Ensure all parent directories have explicit entries
+                    // Ensure ALL ancestor directories have explicit entries
-                    // (js-dos Emscripten FS requires explicit directory entries)
+                    // (Emscripten FS requires every directory in the chain)
                     int idx = entryName.lastIndexOf('/');
-                    if (idx >= 0) {
+                    while (idx >= 0) {
                         String parent = entryName.substring(0, idx + 1);
                         if (addedDirs.add(parent)) {
                             zos.putNextEntry(new java.util.zip.ZipEntry(parent));
                             zos.closeEntry();
                         }
+                        idx = entryName.lastIndexOf('/', idx - 1);
                     }
                     zos.putNextEntry(new java.util.zip.ZipEntry(entryName));
                     Files.copy(f, zos);