[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/app-server/Cargo.toml

@@ -54,6 +54,7 @@ codex-rmcp-client = { workspace = true }
 codex-rollout = { workspace = true }
 codex-sandboxing = { workspace = true }
 codex-state = { workspace = true }
+codex-thread-store = { workspace = true }
 codex-tools = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
 codex-utils-json-to-toml = { workspace = true }