Add workflow metrics endpoint and aggregation with tests

[akgohain]

Motivation

• Provide a backend endpoint to expose workflow-stage and agent-action analytics to consumers via a stable schema.
• Compute common metrics (event counts, approvals/rejections, transitions, timestamps) for operational visibility and reporting.
• Ensure the endpoint behaves predictably when no or sparse events exist by returning safe defaults.

Description

• Added server_api/workflow/metrics.py which implements compute_workflow_metrics and helper timestamp parsing/formatting functions.
• Added server_api/workflow/router.py exposing GET /api/workflows/{workflow_id}/metrics that reads events from app.state.workflow_events_store and returns {"workflow_id", "metrics"}.
• Wired the workflow router into the main app by including the router in server_api/main.py so the endpoint is mounted at runtime.
• Added tests/test_workflow_metrics.py which validates the response schema, safe defaults for empty event lists, and correctness against seeded events.

Testing

• Attempted the requested run uv run pytest -q tests/test_workflow_metrics.py which failed in this environment due to editable pytorch_connectomics package metadata resolution.
• Run the focused test set with PYTHONPATH=. pytest -q tests/test_workflow_metrics.py and all tests passed (3 passed).

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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.