Make model switcher two-stage (#4178)

https://github.com/user-attachments/assets/16d5c67c-e580-4a29-983c-a315f95424ee

codex-rs/tui/src/app_event.rs

@@ -1,5 +1,6 @@
 use std::path::PathBuf;
 
+use codex_common::model_presets::ModelPreset;
 use codex_core::protocol::ConversationPathResponseEvent;
 use codex_core::protocol::Event;
 use codex_file_search::FileMatch;
@@ -60,6 +61,12 @@ pub(crate) enum AppEvent {
         effort: Option<ReasoningEffort>,
     },
 
+    /// Open the reasoning selection popup after picking a model.
+    OpenReasoningPopup {
+        model: String,
+        presets: Vec<ModelPreset>,
+    },
+
     /// Update the current approval policy in the running app and widget.
     UpdateAskForApprovalPolicy(AskForApproval),