Add app-server marketplace upgrade RPC (#19074)

## Summary
- add a v2 `marketplace/upgrade` app-server RPC that mirrors the
existing configured Git marketplace upgrade path
- expose typed request/response/error payloads and regenerate
JSON/TypeScript schema fixtures
- add app-server integration coverage for all, named, already
up-to-date, and invalid marketplace upgrade requests

## Tests
- `just write-app-server-schema`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server marketplace_upgrade`
- `just fix -p codex-app-server-protocol`
- `just fix -p codex-app-server`
- `just fmt`

codex-rs/app-server/tests/common/mcp_process.rs

@@ -49,6 +49,7 @@ use codex_app_server_protocol::ListMcpServerStatusParams;
 use codex_app_server_protocol::LoginAccountParams;
 use codex_app_server_protocol::MarketplaceAddParams;
 use codex_app_server_protocol::MarketplaceRemoveParams;
+use codex_app_server_protocol::MarketplaceUpgradeParams;
 use codex_app_server_protocol::McpResourceReadParams;
 use codex_app_server_protocol::McpServerToolCallParams;
 use codex_app_server_protocol::MockExperimentalMethodParams;
@@ -565,6 +566,15 @@ impl McpProcess {
         self.send_request("marketplace/remove", params).await
     }
 
+    /// Send a `marketplace/upgrade` JSON-RPC request.
+    pub async fn send_marketplace_upgrade_request(
+        &mut self,
+        params: MarketplaceUpgradeParams,
+    ) -> anyhow::Result<i64> {
+        let params = Some(serde_json::to_value(params)?);
+        self.send_request("marketplace/upgrade", params).await
+    }
+
     /// Send a `plugin/install` JSON-RPC request.
     pub async fn send_plugin_install_request(
         &mut self,