Re-architect around pipelines
Removed loosely structured workflows. Now compose multistep work as pipeline modules, e.g. base.pipelines.segment, with the following blocks:
- input parameters (Pydantic model)
- output record (Pydantic model)
- API mapping and docstring; also any special input validation that doesn't play well Pydantic, and special exception routing
- pipeline logic function, which pushes results onto PipelineTrace
Refactored existing base and ilastik "workflows" into this pattern.