Leverage state DB metadata for thread summaries (#10621)

Summary:
- read conversation summaries and cwd info from the state DB when
possible so we no longer rely on rollout files for metadata and avoid
extra I/O
- persist CLI version in thread metadata, surface it through summary
builders, and add the necessary DB migration hooks
- simplify thread listing by using enriched state DB data directly
rather than reading rollout heads

Testing:
- Not run (not requested)

codex-rs/state/migrations/0005_threads_cli_version.sql

@@ -0,0 +1 @@
+ALTER TABLE threads ADD COLUMN cli_version TEXT NOT NULL DEFAULT '';