fix(cli): revert broken merge and stabilize atomic-write-metadata - #109

Reverts broken merge d58c2f2 (merge: preserve active lane while absorbing remote) and applies atomic-write-metadata contract and test gates.

• Revert merge: d58c2f2
• Apply: atomic_file.py, atomic_file_state.py, test_atomic_file_contract.py, test_atomic_file_guarded.py, test_file_derived_contracts.py
• Modify: flextcliutilitiesfiles_part_02.py, file_tools.py, test_files_cov.py

Summary by cubic

Reverts the broken "preserve active lane while absorbing remote" merge so CLI behavior returns to its pre-merge state, and stabilizes the atomic-write metadata contract with test gates.

Bug Fixes

• Drops the broken merge's lane-preserving logic.
• Atomic-write metadata now follows an enforced contract, guarded by new contract and derived-contract tests.

^{Written for commit 38b79b7. Summary will update on new commits.}