feat(skills): add transactional native skill lifecycle

[rudijetson]

Summary

• replace best-effort native skill copying with one ownership-aware transactional lifecycle
• reconcile install, update, explicit sync, check, host status, and removal across Codex, Claude, Gemini, and Antigravity
• bind receipts to source identity, complete canonical-package digest, and rendered-tree digest
• preserve drifted or unmanaged trees unless exact scoped force is authorized
• fail closed for symlink, receipt, rollback, and concurrent-reconciliation hazards

Risk

High. This changes persistent host-native skill trees and ownership receipts. The implementation stages replacements, validates complete trees, atomically promotes target/receipt state, and preserves recoverable state on conflicts.

Verification

• focused tests: 89/89
• full tests: 774/774
• hostile review regressions: 6/6
• reproducible build: passed
• debt scan: 0 findings
• package dry run: 6 files
• independent review: Standards, Spec, Proof, Overall pass

Generated artifact

Tracked dist/index.cjs is isolated in dedicated build commits. Final SHA-256: 32733e510d83b50f707a13e0ecb4bbe3d8c3a320cb8ac8d04f453ed652eff02b.

Rollback

Revert the merge commit. If the installed runtime also needs rollback, use the machine-local backups recorded in the compliance ledger; do not overwrite native trees without revalidating ownership receipts.

Fixes #37