[WIP] Add staged architectural initiative checkpoints

[smallmou]

Summary

• add isolated, persisted staged initiative checkpoints with strict stage gates and production-incumbent isolation
• trigger architectural escape episodes after episode-count or promotion-drought thresholds
• preserve staged continuity across blocked episodes and track initiative outcomes
• reap direct and detached episode process groups without affecting unrelated processes
• escalate a checkpoint evidence plan after three blocked continuation attempts, requiring variance-aware paired validation without weakening production gates

Validation

• python3.10 -m unittest long_horizon.test_staged_checkpoint long_horizon.test_journal_wiki_attribution
• detached-helper cleanup and unrelated-process isolation regressions
• python3.10 -m py_compile long_horizon/campaign.py