[codex] Add local thread store listing (#17824)

Builds on top of #17659 

Move the filesystem + sqlite thread listing-related operations inside of
a local ThreadStore implementation and call ThreadStore from the places
that used to perform these filesystem/sqlite operations.

This is the first of a series of PRs that will implement the rest of the
local ThreadStore.

Testing:
- added unit tests for the thread store implementation
- adjusted some unit tests in the realtime + personality packages whose
callsites changed. Specifically I'm trying to hide ThreadMetadata inside
of the local implementation and make ThreadMetadata a sqlite
implementation detail concern rather than a public interface, preferring
the more generate StoredThread interface instead
- added a corner case test for the personality migration package that
wasn't covered by the existing test suite
- adjust the behavior of searched thread listing to run the existing
local rollout repair/backfill pass _before_ querying SQLite results, so
callers using ThreadStore::list_threads do not miss matches after a
partial metadata warm-up

codex-rs/core/tests/suite/realtime_conversation.rs

@@ -194,10 +194,16 @@ async fn seed_recent_thread(
     let db = test.codex.state_db().context("state db enabled")?;
     let thread_id = ThreadId::new();
     let updated_at = Utc::now();
+    let rollout_path = test
+        .codex_home_path()
+        .join(format!("rollout-{thread_id}.jsonl"));
+    // This helper seeds SQLite metadata directly. Local listing drops stale metadata rows whose
+    // rollout path no longer exists, so create the placeholder path that the test metadata points
+    // at without exercising rollout writing in this realtime-context test.
+    std::fs::write(&rollout_path, "")?;
     let mut metadata_builder = codex_state::ThreadMetadataBuilder::new(
         thread_id,
-        test.codex_home_path()
-            .join(format!("rollout-{thread_id}.jsonl")),
+        rollout_path,
         updated_at,
         SessionSource::Cli,
     );