Make advanced reasoning selection explicit in the TUI (#32746)

## Why

`Max` and `Ultra` consume usage limits faster than standard reasoning levels, so they should not be selected accidentally while navigating the normal effort scale.

## What changed

- Move `Max` and `Ultra` behind a `More reasoning…` entry with a dedicated warning and descriptions.
- Keep the reasoning shortcuts from silently increasing into advanced efforts.
- Apply `Ultra` to the active conversation without changing defaults for new threads, while preserving it across mode switches and thread resumes.
- Record applied thread settings in thread metadata, including explicit clearing of reasoning effort, so resumed threads restore their latest model settings unless the user supplied an override.

## Testing

- Add TUI coverage for the advanced picker, shortcuts, Plan mode, configuration defaults, and resumed conversations.
- Add app-server and thread-store coverage for persisting, clearing, and restoring model and reasoning settings.

GitOrigin-RevId: 6708c7c2e8d38f491bf63000ea34f83476afdfe6

codex-rs/tui/src/app_event.rs

@@ -741,6 +741,17 @@ pub(crate) enum AppEvent {
         model: ModelPreset,
     },
 
+    /// Open the explicit Max/Ultra reasoning selection popup for a model.
+    OpenAdvancedReasoningPopup {
+        model: ModelPreset,
+    },
+
+    /// Apply an advanced reasoning effort to the active conversation without changing defaults.
+    ApplyAdvancedReasoning {
+        model: String,
+        effort: ReasoningEffort,
+    },
+
     /// Open the Plan-mode reasoning scope prompt for the selected model/effort.
     OpenPlanReasoningScopePrompt {
         model: String,