menubar-pet: the Swift menu-bar app #18

The third face. See docs/superpowers/specs/2026-09-04-menubar-pet-design.md.

Done when:

• A sibling SwiftPM package builds an executable, and a script assembles a .app around it with LSUIElement set, so there is no Dock icon and no window.
• An NSStatusItem shows the face; the menu carries name, stage, age, the cemetery and Quit.
• A timer polls pet-life every 5 seconds, resolving it next to the app's own binary first and then PATH.
• A missing or failing pet-life shows a neutral glyph and says the daemon is not reachable, rather than a stale pet.
• The pre-push hook builds it, so a package outside the gate cannot rot.