Add parallel codex-exec workers

[SetraTheXX]

Summary

Adds guarded parallel worker execution for Coordinator Mode.

Added

• cewp run dispatch exec workers --adapter codex-exec --yes --parallel
• cewp run dispatch pipeline --adapter codex-exec --yes --parallel
• Parallel preflight for separate worktrees and non-overlapping allowedFiles

Safety

• Reviewer does not run in parallel
• No auto finalize
• No merge/push/publish
• Parallel mode blocks same worktree and allowedFiles overlap
• Worker output handoff remains isolated via .cewp-worker-output/

Verification

• Worker A/B parallel execution passed
• Scope and forbidden file checks passed
• Negative preflight tests passed
• npm pack --dry-run passed

Note

Full reviewer step was blocked by Codex CLI usage limit during final smoke, not by implementation failure. Re-run full pipeline smoke before merge.

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.