fix: use dirStream.toList() instead of method reference cast in existsIgnoreCase

Iterable<Path> cast on dirStream::iterator method reference fails
in some Java environments. Stream.toList() (Java 16+) is cleaner
and guaranteed to compile.

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

@@ -644,13 +644,12 @@ public class UploadResource {
             for (int i = 0; i < parts.length; i++) {
                 String part = parts[i];
                 if (part.isEmpty()) {
-                    // Trailing separator means directory — check if current is a dir
                     if (i == parts.length - 1) return Files.isDirectory(current);
                     continue;
                 }
                 Path found = null;
                 try (var dirStream = Files.list(current)) {
-                    for (Path entry : (Iterable<Path>) dirStream::iterator) {
+                    for (Path entry : dirStream.toList()) {
                         if (entry.getFileName().toString().equalsIgnoreCase(part)) {
                             found = entry;
                             break;