Add legacy rollout migration to paginated history (#37175)

## What changed

- Add `LocalThreadStore::migrate_rollouts` with dry-run and apply modes,
  optional thread selection, throughput limiting, and per-rollout outcomes.
- Canonicalize legacy JSONL records into paginated history while preserving
  model-visible conversation context, including compressed rollouts and copied
  fork history.
- Publish replacements atomically and journal migrations so interrupted SQLite
  projections can be recovered. Coordinate migration with rollout compression
  and skip rollouts with active writers.
- Make paginated history a one-way SQLite promotion so stale metadata cannot
  downgrade a migrated thread.

## Testing

- Cover legacy record normalization, dry runs, idempotency, malformed input,
  compressed rollouts, active writers, interrupted migration recovery, and a
  cold app-server resume after migration.

GitOrigin-RevId: b9991b659f28ebb52da39ce62e8b4e0bae2ba2bb

codex-rs/thread-store/src/lib.rs

@@ -24,6 +24,11 @@ pub use live_thread::LiveThread;
 pub use live_thread::LiveThreadInitGuard;
 pub use local::LocalThreadStore;
 pub use local::LocalThreadStoreConfig;
+pub use local::RolloutMigrationMode;
+pub use local::RolloutMigrationOptions;
+pub use local::RolloutMigrationOutcome;
+pub use local::RolloutMigrationReport;
+pub use local::RolloutMigrationStatus;
 pub use queue_store::LocalQueueStore;
 pub use queue_store::QueueStore;
 pub use store::ThreadStore;