Refactor: Use MongoDB _id for messages, pipeline_id_index for components, standardize outputs to result:{text:{}} format

feat: API response corrections - add message_id, component tracking, and error handling

feat: Unified pipeline lifecycle - single S3 file per pipeline - Pipeline now stored in S3 with pipeline_id at creation - Proposals stored in S3, only reference in MongoDB - Results appended to same S3 file on completion - Workflow save uses pipeline_id, works at any stage - pipelines_history now in session API response

feat: Implement V3 Architecture - S3 + Normalized MongoDB