Derive collaboration settings from turn context (#32900)

## Why

`TurnContext` stored model and reasoning settings both as resolved turn fields and inside `CollaborationMode`, requiring the copies to stay synchronized when the model changed.

## What changed

- Store the mode and collaboration-mode developer instructions directly on `TurnContext`.
- Reconstruct `CollaborationMode` from those values plus the turn's current model and reasoning effort when callers need it.
- Read the mode directly for plan-mode checks, lifecycle events, and telemetry.

GitOrigin-RevId: b8fccafdd5d5cbccc84bc70d542588087ddf0093

codex-rs/core/src/session/review.rs

@@ -130,7 +130,10 @@ pub(super) async fn spawn_review_thread(
         timezone: parent_turn_context.timezone.clone(),
         app_server_client_name: parent_turn_context.app_server_client_name.clone(),
         developer_instructions: None,
-        collaboration_mode: parent_turn_context.collaboration_mode.clone(),
+        mode: parent_turn_context.mode,
+        collaboration_mode_developer_instructions: parent_turn_context
+            .collaboration_mode_developer_instructions
+            .clone(),
         multi_agent_version: MultiAgentVersion::Disabled,
         personality: parent_turn_context.personality,
         approval_policy: parent_turn_context.approval_policy.clone(),