fix: Cascading deletes to files when deleting users (#12155)

* fix: Cascading delets to files when deleting users

* Add a test for delete cascades

* Ensure in-db cascade

* [autofix.ci] apply automated fixes

* Update 0e6138e7a0c2_add_ondelete_cascade_to_file_user_id_fk.py

* Update 0e6138e7a0c2_add_ondelete_cascade_to_file_user_id_fk.py

* Update src/backend/base/langflow/alembic/versions/0e6138e7a0c2_add_ondelete_cascade_to_file_user_id_fk.py

Co-authored-by: Copilot <[email protected]>

* Update test_user.py

* Update src/backend/tests/unit/test_user.py

Co-authored-by: Copilot <[email protected]>

* Update src/backend/base/langflow/alembic/versions/0e6138e7a0c2_add_ondelete_cascade_to_file_user_id_fk.py

Co-authored-by: Copilot <[email protected]>

* Update test_user.py

* Update src/backend/tests/unit/test_user.py

Co-authored-by: Copilot <[email protected]>

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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Copilot <[email protected]>