fix: use Files.write() for byte[] return from buildCdOnlyJsdosJson

Files.writeString expects CharSequence, but buildCdOnlyJsdosJson
returns byte[]. Changed to Files.write() which accepts byte[].

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

@@ -454,7 +454,7 @@ public class UploadResource {
         } else {
             // CD-only game — no executable, mount CD and show a DOS prompt
             Files.writeString(jsdos.resolve("dosbox.conf"), buildCdOnlyDosboxConf(cdImages));
-            Files.writeString(jsdos.resolve("jsdos.json"), buildCdOnlyJsdosJson());
+            Files.write(jsdos.resolve("jsdos.json"), buildCdOnlyJsdosJson());
         }
 
         // ZIP it up directly from extractDir (no temp copy)