Add marketplace display names to plugin/list (#14861)

Add display_name support to marketplace.json.

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -3276,6 +3276,7 @@ pub struct SkillsListEntry {
 pub struct PluginMarketplaceEntry {
     pub name: String,
     pub path: AbsolutePathBuf,
+    pub display_name: Option<String>,
     pub plugins: Vec<PluginSummary>,
 }