Fix backend execution import error and Airflow callback typing

[fuzziecoder]

Motivation

• The backend failed to import due to a duplicated/broken initialize_execution declaration and background execution logic that could overwrite callback-preserved context and logs.
• Airflow callback payloads were being parsed with a duplicated callback_type field that downgraded the enum type to a plain str, breaking code that expects enum values.

Description

• Removed the duplicated initialize_execution(...) declaration in backend/api/routes/executions.py and kept a single, well-formed implementation to resolve import-time syntax errors.
• Simplified background execution persistence in execute_pipeline_background to use a single context/log merge path and avoid redundant overwrites before saving the execution record.
• Fixed the AirflowCallbackRequest schema in backend/api/schemas.py by removing the duplicate callback_type field so the value remains typed as AirflowCallbackTypeSchema.
• Changes restore correct handling of Airflow trigger/callback flows and ensure callback handlers can access .value on the enum type.

Testing

• Ran python -m compileall -q backend to verify modules compile successfully, which completed without errors.
• Ran PYTHONPATH=. pytest -q backend/tests/test_airflow_integration.py and all tests passed (5 passed) with only unrelated warnings.
• Imported the FastAPI app with from backend.main import app and verified the application loads and registers routes (verified len(app.routes)).

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Codex Task

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Project	Deployment	Actions	Updated (UTC)
flexi-roaster	Ready	Preview, Comment	Feb 23, 2026 5:17pm

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✅ Devin Review: No Issues Found

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