Add hosted Airflow MCP migration review flow

[peterpark-db]

Summary

• add hosted Airflow inputs for UC Volumes, Workspace directories, inline DAG definitions, and local source paths
• make Airflow MCP migration pause before packaging when reconciled gaps remain, then resume only from the reviewed agentic report
• classify leaf-resolvable, structural, and unsupported source-semantic gaps so the v1 leaf contract is represented honestly
• prevent branch, short-circuit, TaskGroup, SubDag, trigger-rule, and task-policy gaps from accepting leaf replacements
• preserve the existing ADF migration and legacy agentic merge workflows
• document hosted Airflow source delivery and reviewed-gap completion states

Structural graph rewrites and multi-task replacement remain outside contract v1; no GraphPatch implementation is included.

Safety

• inline Airflow sources accept only normalized relative .py paths and string content
• traversal, backslashes, normalized duplicate paths, non-Python files, and oversized UTF-8 payloads are rejected
• temporary source trees are cleaned after each command
• unresolved Airflow gaps never proceed directly to package
• reviewed reports are passed explicitly through the existing package validation gate
• migrations retaining reviewed placeholders report completed_with_reviewed_gaps, not completed

Validation

• uv run --frozen pytest -q tests/unit — 1244 passed
• uv run --frozen pytest -q tests/integration -m "not slow and not integration" — 141 passed, 16 deselected, 6 xfailed
• uv run --frozen ruff format --check src tests
• uv run --frozen ruff check src tests
• uv run --frozen mypy src/flowx/
• git diff --check