Hydrate recommended plugin metadata on selection (#39143)

## What changed

- Fetch recommendations from the Codex-specific `/ps/plugins/suggested/codex` endpoint and parse its compact response shape.
- Fetch the selected plugin's details before presenting an install request, using them to verify availability and populate connector metadata.
- Skip install elicitation when the selected recommendation is no longer available, and return a retryable response when its metadata cannot be verified.

## Testing

- Cover the new recommendation route and response shape.
- Cover metadata hydration for available plugins and rejection of unavailable plugins.

GitOrigin-RevId: 2b0e2d70572aae2b7cd8e458b42e9dd14be3dbaf

codex-rs/core-plugins/src/manager.rs

@@ -1373,7 +1373,7 @@ impl PluginsManager {
                     description: None,
                     has_skills: false,
                     mcp_server_names: Vec::new(),
-                    app_connector_ids: plugin.app_connector_ids,
+                    app_connector_ids: Vec::new(),
                 })
             })
             .collect();