Add workflow evidence export utility for research notes

[akgohain]

Motivation

• Provide a stable, machine-readable JSON export of workflow evidence for paper/research notes including stage progression, agent proposal/approval summary, and a key-event timeline snippet.
• Make it easy to run locally via a simple CLI and to write exports into a research docs folder with a stable version key for reproducibility.

Description

• Add server_api/workflow/data_access.py which implements load_workflow_payload and WorkflowDataError to validate and normalize workflow JSON events.
• Add server_api/workflow/evidence_export.py which implements build_workflow_evidence_export, export_workflow_evidence, a CLI entrypoint, and EVIDENCE_EXPORT_VERSION = "1.0", and emits the required stage_progression_summary, agent_proposal_approval_summary, and key_event_timeline_snippet sections.
• Export the API from server_api/workflow/__init__.py, add docs at docs/research/workflow-evidence-export.md describing how to run the exporter and where outputs are written, and add unit tests in tests/test_workflow_evidence_export.py that use a seeded fixture.
• The CLI writes the JSON exactly to the provided --output path and creates parent directories automatically.

Testing

• Ran python -m pytest -q tests/test_workflow_evidence_export.py which passed (2 passed).
• Running uv run pytest -q tests/test_workflow_evidence_export.py failed in this environment due to missing editable dependency project metadata for pytorch-connectomics so that invocation may require installing or fixing that dependency for CI-style runs.
• The new unit tests validate the presence of the version key and the three required sections, the summarized counts for proposals/decisions, and that the exporter writes the expected output file.

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Codex Task

[akgohain]

Consolidated into draft PR #165 (feat/codex-wave-integration). Closing this source draft to keep review in one place.