fix(record): validate macOS runner stop and finalized video

[thymikee]

Problem

The macOS recording backend uses the same runner recordStop flow as physical iOS, but currently ignores the stop outcome and proceeds without validating the finalized local video.

PR #1238 makes the physical-iOS backend fail when either:

• the runner reports recordStop did not succeed, or
• the copied MP4 is not stable/playable.

The macOS backend still calls stopRunnerRecordingBestEffort without consuming its boolean result and does not run waitForStableFile / isPlayableVideo before overlay processing and artifact publication. This can report success for a failed runner stop or an invalid MP4.

Scope

Bring the macOS runner recording backend to behavioral parity while preserving the existing RecordingBackend.stop seam. Avoid forcing a universal cross-platform finalization abstraction: simulator, Android, physical iOS, and macOS materialize recordings differently.

Acceptance criteria

• A macOS runner recordStop failure returns COMMAND_FAILED.
• A stable, playable local MP4 is required before overlay processing or artifact publication.
• Failure clears recording session state and publishes no artifact.
• Successful macOS recordings retain current overlay and artifact behavior.
• Provider-level coverage exercises success, runner-stop failure, and invalid-video outcomes through the production route.
• Live macOS verification confirms the finalized artifact is playable.

Context

Follow-up discovered while reviewing and tightening #1238. The physical-iOS implementation is intentionally backend-specific; this issue closes the remaining consistency gap for the other Apple runner recording backend.