[codex] Add Workbench health and journal diagnostics

[jiweiqi]

Summary

Adds Workbench readiness and journal diagnostics so agents can inspect project state and stop cleanly when a journal reports failure.

What changed

• Adds health, UI mode, systems summary, and project identity inspect targets.
• Converts parsed journal ok=false results into outer run failure with workbench.journal.result_failed diagnostics.
• Adds CI/release scaffolding, sanitized workflow docs, and a Workbench-to-Mechanical handoff smoke workflow.
• Adds focused tests for journal failure handling and packaged skill content.

Validation

• CI passed for the pull request.
• Targeted driver tests passed for journal diagnostics and systems summary behavior.