setup-curator-guard-targets-retrofits-not-new-from-spec-skills

The setup-curator guard correctly fires on substantive edits to pre-existing skills (retrofitting fusion contracts onto skills that existed before the spec) but should not block new-from-spec skill creation (skills being built for the first time per an approved phase plan). Pre-approved phase build-outs do not require a curator invocation per skill — only the phase-entry routing decision is sufficient. Retroactively adding fusion contracts to existing platform skills triggers the guard for good reason.