Expose environment status through app-server (#32920)

## What changed

- Add the experimental `environment/status` request for inspecting a configured environment without starting or reconnecting it.
- Report `ready`, `pending`, `disconnected`, or `unknown`, including error details for disconnected and unknown environments.
- Probe ready remote environments over their existing exec-server connection.

## Testing

- Add an app-server integration test covering local and remote ready, pending, disconnected, and unknown environments.

GitOrigin-RevId: 397bba603aa9e0b59008ee6cb7cbde46e357652c

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

@@ -956,6 +956,13 @@ client_request_definitions! {
         serialization: global_shared_read("environment"),
         response: v2::EnvironmentInfoResponse,
     },
+    #[experimental("environment/status")]
+    /// Reads the current status of a configured execution environment.
+    EnvironmentStatus => "environment/status" {
+        params: v2::EnvironmentStatusParams,
+        serialization: global_shared_read("environment"),
+        response: v2::EnvironmentStatusResponse,
+    },
 
     McpServerOauthLogin => "mcpServer/oauth/login" {
         params: v2::McpServerOauthLoginParams,