Agent Skills: toggle-sibling-libraries

Toggle a Swift Package.swift between the local-sibling-checkout development pattern and a clean remote-only release pattern. Use this skill whenever you need to flip Package.swift in or out of the `sibling(...)` helper-function pattern — for example, before tagging a release the dependencies must be pinned to remote-only, and on a fresh `-dev` development cycle they must go back to sibling-aware. Also trigger on phrases like "switch to remote deps", "remove the sibling helper", "restore sibling pattern", "make Package.swift release-ready", "flip to dev-mode deps", or any time the user references the `sibling()` helper or the `useLocalSiblings` constant. Only intrusive-memory/* dependencies participate in the sibling pattern; all other dependencies are left untouched.