Add finalization-only cleanup gate for provisional scratch artifacts

[mmprotest]

Motivation

• Prevent temporary files created by model-driven shell probing from lingering in the repo while avoiding changes to model behavior or verification flow.
• Ensure cleanup is conservative, reversible, and executed only once after a successful verification pass.

Description

• Add runner-owned provenance state: _provisional_scratch_candidates, _explicit_mutation_created_paths, and _cleanup_summary on the Runner to track Bash-created files and explicit Write/Patch-created files.
• Capture provenance at the normal tool boundary by snapshotting repo files before/after Bash in execute_tool_with_lifecycle and adding newly-created files to the provisional set while recording Write/Patch created paths separately in state_tooling.py.
• Implement cleanup_provisional_scratch_artifacts in state_runtime.py that conservatively filters eligible candidates (must be provenance-backed, regular file, inside repo, not explicit edits, not under source/test/pkg roots, root detection confident), backs them up, removes them, reruns existing run_validation, and restores files on any failure/error.
• Invoke the cleanup exactly once in the finalization path (in _finish_bounded after run_post_execution_validation and before final summary write) and propagate cleanup telemetry into final_summary.json via DebugRecorder.write_final_summary without adding a new telemetry system.
• Add focused tests in tests/test_scratch_cleanup_gate.py covering keep/restore, git untracked handling, exclusion of Write-created files, and source/tests exclusions.

Testing

• Ran pytest -q tests/test_scratch_cleanup_gate.py and all tests passed (4 passed).
• Verified the cleanup call site is singular with rg -n "cleanup_provisional_scratch_artifacts\(" villani_code, confirming the helper is invoked from exactly one final post-success location.

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Codex Task