fix: use serde for ManifestKind

src/model/manifest_kind.rs

@@ -1,6 +1,9 @@
+use serde::{Deserialize, Serialize};
+
 use crate::model::{ModPack, SimpleMod};
 
-#[derive(Debug)]
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(rename_all = "snake_case")]
 pub enum ManifestKind {
     V1(Vec<SimpleMod>),
     V2(ModPack),