feat: Add plugin share checkout (#22435)

Adds plugin/share/checkout to turn a shared remote plugin into a local
working copy under ~/plugins/<name>.

Registers the copy in the managed personal marketplace and records the
remote-to-local mapping for later share/save flows.

---------

Co-authored-by: Codex <noreply@openai.com>

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

@@ -242,6 +242,26 @@ pub struct PluginShareListResponse {
     pub data: Vec<PluginShareListItem>,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct PluginShareCheckoutParams {
+    pub remote_plugin_id: String,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct PluginShareCheckoutResponse {
+    pub remote_plugin_id: String,
+    pub plugin_id: String,
+    pub plugin_name: String,
+    pub plugin_path: AbsolutePathBuf,
+    pub marketplace_name: String,
+    pub marketplace_path: AbsolutePathBuf,
+    pub remote_version: Option<String>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]