Persist thread_dynamic_tools in sqlite and read first from it. Fall back
to rollout files if it's not found. Persist dynamic tools to both sqlite
and rollout files.
Saw that new sessions get populated to db correctly & old sessions get
backfilled correctly at startup:
```
celia@com-92114 codex-rs % sqlite3 ~/.codex/state.sqlite \ "select thread_id, position,name,description,input_schema from thread_dynamic_tools;"
019c0cad-ec0d-74b2-a787-e8b33a349117|0|geo_lookup|lookup a city|{"properties":{"city":{"type":"string"}},"required":["city"],"type":"object"}
....
019c10ca-aa4b-7620-ae40-c0919fbd7ea7|0|geo_lookup|lookup a city|{"properties":{"city":{"type":"string"}},"required":["city"],"type":"object"}
```
Celia Chen