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/chatwidget/session_flow.rs

@@ -83,6 +83,9 @@ impl ChatWidget {
             Some(session.reasoning_effort.clone()),
             /*developer_instructions*/ None,
         );
+        if session.reasoning_effort == Some(ReasoningEffortConfig::Ultra) {
+            self.set_plan_mode_reasoning_effort(Some(ReasoningEffortConfig::Ultra));
+        }
         match session.collaboration_mode.as_deref() {
             Some(collaboration_mode) => {
                 self.set_effective_collaboration_mode(collaboration_mode.clone());