Review mode core updates (#3701)

1. Adds the environment prompt (including cwd) to review thread
2. Prepends the review prompt as a user message (temporary fix so the
instructions are not replaced on backend)
3. Sets reasoning to low
4. Sets default review model to `gpt-5-codex`

codex-rs/core/src/lib.rs

@@ -88,6 +88,7 @@ pub use codex_protocol::config_types as protocol_config_types;
 
 pub use client::ModelClient;
 pub use client_common::Prompt;
+pub use client_common::REVIEW_PROMPT;
 pub use client_common::ResponseEvent;
 pub use client_common::ResponseStream;
 pub use codex_protocol::models::ContentItem;