refactor(codebase-health): delegate audit fix phases to implementation/verification lanes

[kyle-sexton]

audit Phases 4-7 (fix/verify/self-review/retro) duplicate lanes other plugins own. Keep audit read-only through Phase 3 per the codified audit contract; delegate remediation to implementation:implement + verification:confirm (soft refs or dependencies per the cross-plugin rule).

Origin: skill-name audit + interview, contract at docs/topics/shadowed-skill-renames/PLAN.md (PR #256).

[kyle-sexton]

This was generated by AI during triage (historic normalization, rule 8g).

Sites + fix pattern: plugins/codebase-health/skills/audit/SKILL.md (cut Phases 4-7, keep read-only through Phase 3), plugins/codebase-health/skills/audit/templates/checklist.md (drop the now-delegated phase items), soft-ref/dependency note pointing at implementation:implement + verification:confirm per the cross-plugin rule. No design decision — direction fully specified in the issue body.

[kyle-sexton]