core(rollout): extract rollout module, add listing API, and return file heads (#1634)

- Move rollout persistence and listing into a dedicated module:
rollout/{recorder,list}.
- Expose lightweight conversation listing that returns file paths plus
the first 5 JSONL records for preview.

codex-rs/core/Cargo.toml

@@ -41,7 +41,7 @@ similar = "2.7.0"
 strum_macros = "0.27.2"
 tempfile = "3"
 thiserror = "2.0.16"
-time = { version = "0.3", features = ["formatting", "local-offset", "macros"] }
+time = { version = "0.3", features = ["formatting", "parsing", "local-offset", "macros"] }
 tokio = { version = "1", features = [
     "io-std",
     "macros",