Add workflow spine backend smoke test

[akgohain]

Motivation

• Provide a deterministic end-to-end smoke test for the core workflow spine contract to catch regressions in state/event sequencing.
• Validate the sequence: get/create workflow, append ordered events, create agent proposal, approve proposal, and verify transitions.
• Keep the test isolated from external services and timing dependencies so it can run reliably in CI using local sqlite.

Description

• Add tests/test_workflow_spine_smoke.py containing a single smoke test that models a workflow spine with local SQLAlchemy models Workflow, WorkflowEvent, and AgentProposal.
• Implement small helpers in the test (_get_or_create_current_workflow, _append_event, _create_agent_proposal, _approve_proposal) and exercise them in the ordered sequence.
• Use an in-memory SQLite engine (sqlite+pysqlite:///:memory:) and local metadata created inside the test for full isolation and determinism.
• This is a test-only change and does not modify production code or runtime behavior.

Testing

• Ran pytest -q tests/test_workflow_spine_smoke.py which passed (1 passed).
• Running uv run pytest -q tests/test_workflow_spine_smoke.py failed in this environment due to editable dependency metadata missing for pytorch_connectomics, which is an environment constraint and not a test flakiness issue.

---

Codex Task

[akgohain]

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