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/exec-server/src/environment.rs

@@ -297,19 +297,6 @@ impl EnvironmentManager {
         environment_ids
     }
 
-    /// Returns every configured environment id in deterministic order.
-    pub fn environment_ids(&self) -> Vec<String> {
-        let mut environment_ids = self
-            .environments
-            .read()
-            .unwrap_or_else(std::sync::PoisonError::into_inner)
-            .keys()
-            .cloned()
-            .collect::<Vec<_>>();
-        environment_ids.sort_unstable();
-        environment_ids
-    }
-
     /// Returns the local environment instance when one is configured.
     pub fn try_local_environment(&self) -> Option<Arc<Environment>> {
         self.local_environment.as_ref().map(Arc::clone)