Optimistic versioning if CAS is insufficient

[chuanman2707]

Roadmap parent issue for v2.2 Phase 5 conditional work.

Source: docs/superpowers/specs/capyinn-concurrency-spec-v2.2.md

When to start:

• Only after Phase 3 proves CAS-by-status and DB constraints are not enough for a specific aggregate.

Scope:

• Evaluate CAS gaps before adding version columns #87
• Add targeted optimistic version columns and conflict handling if needed #88
• Add optimistic versioning regression tests if versions are introduced #89

Exit criteria:

• Either no version columns are needed, or targeted versioning is implemented with tests and migration guardrails.