## What changed
- Add `threadSection/create`, `threadSection/update`, and `threadSection/delete` app-server methods, with generated protocol schemas and TypeScript bindings.
- Persist custom sections in SQLite with stable UUIDv7 identities, trim and validate display names, and prevent renaming or deleting the built-in pinned section.
- Delete sections transactionally and return their active and archived threads to the unsectioned list.
- Serialize section mutations with section listing so concurrent requests observe ordered updates.
## Testing
- Cover section persistence across restarts, ordered renames, member cleanup on deletion, invalid requests, unsupported stores, and thread-store/state-runtime behavior.
GitOrigin-RevId: dc9a4be283c21dbc93ab1829eafc4825d8df6575
