feat: wire plan-reviewer as automatic gate after PLAN completion

[JeremyDev87]

Purpose

Automatically dispatch plan-reviewer (#793) as subAgent after PLAN is created, before transitioning to ACT. Creates a quality gate that catches shallow plans.

Changes

• packages/rules/.ai-rules/rules/core.md — Add plan-review step between PLAN and ACT
• packages/rules/.ai-rules/adapters/claude-code.md — Document auto-review dispatch

Acceptance Criteria

• plan-reviewer auto-dispatched after PLAN completion
• Critical/High findings block ACT transition
• Medium/Low findings noted but don't block
• Depends on feat: add plan-reviewer agent and plan-and-review skill for worker plan validation #793 (plan-reviewer agent exists)
• Can be merged independently