- split settings module into per-struct files
- add DatabaseSettings with default in-memory SQLite path
- implement RelayApi struct with GET /relays and POST
/relays/{id}/toggle
- wire create_relay_controller and create_label_repository into
Application::build() with mock/real selection via cfg!(test) || CI
- register RelayApi in OpenApiService alongside existing APIs
Add complete SQLite implementation of RelayLabelRepository trait with
all CRUD operations (get_label, save_label, delete_label, get_all_labels).
Key changes:
- Create infrastructure entities module with RelayLabelRecord struct
- Implement TryFrom traits for converting between database records and domain types
- Add From<sqlx::Error> and From<RelayLabelError> for RepositoryError
- Write comprehensive functional tests covering all repository operations
- Verify proper handling of edge cases (empty results, overwrites, max length)
TDD phase: GREEN - All repository trait tests now passing with SQLite implementation
Ref: T036 (specs/001-modbus-relay-control/tasks.md)
