Forward-port workflow wave onto current main

[akgohain]

Summary

• forward-port the workflow spine and workflow-aware agent changes onto current main
• add workflow metrics, export-bundle, evidence-export, hotspot proposal, and correction-impact plumbing
• add request lifecycle logging for chat and wire the workflow UX into the current frontend
• fix the editable connectomics package source naming so uv run pytest resolves cleanly

Key Changes

• backend workflow session/event models, router, service, metrics, bundle export, and evidence export
• workflow-linked EHTool and inference/training/visualization event wiring
• structured chat logging in the FastAPI entrypoint
• workflow context, timeline filters, and proposal cards in the client
• backend/frontend tests covering routes, metrics, exports, logging, timeline filters, and proposal cards

Verification

• uv run pytest -q tests/test_workflow_routes.py tests/test_workflow_spine_smoke.py tests/test_chat_logging_fields.py tests/test_workflow_metrics.py tests/test_workflow_export_bundle.py tests/test_workflow_evidence_export.py
• uv run pytest -q tests/test_pytc_runtime_routes.py tests/test_worker_model_service.py
• npm --prefix client test -- --watchAll=false --runInBand
• npm --prefix client run build