Add workflow spine end-to-end smoke test

[akgohain]

Motivation

• Add a deterministic, backend-level smoke test that validates the core workflow spine sequence (get/create workflow, append ordered events, create agent proposal, approve proposal, and verify persisted state).
• Keep the test isolated and non-flaky by running against a local sqlite DB and removing external/async dependencies from the chatbot pipeline.

Description

• Add tests/test_workflow_spine_smoke.py which implements a single end-to-end smoke test exercising the full workflow spine sequence.
• Use a local temporary sqlite database and override FastAPI's get_db dependency to isolate state to the test.
• Inject a deterministic fake chatbot chain (_DeterministicChain) and patch server_api.main._ensure_chatbot, server_api.main.chain, and server_api.main._reset_search to avoid external LLM/async flakiness.
• Guard imports with pytest.importorskip("tifffile") so environments missing optional EHTool deps skip the test cleanly.

Testing

• Ran uv run pytest -q tests/test_workflow_spine_smoke.py which failed in this environment before collection due to an unrelated editable package metadata error for pytorch_connectomics.
• Ran python -m pytest -q tests/test_workflow_spine_smoke.py before adding the skip-guard which failed during collection with ModuleNotFoundError: No module named 'tifffile'.
• After adding pytest.importorskip("tifffile"), re-ran python -m pytest -q tests/test_workflow_spine_smoke.py and the test was skipped in this environment because tifffile is not installed, with no assertion failures in the test logic itself.

---

Codex Task

[akgohain]

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