chore(goal-loop): rebind goal-loop-preview off Cmd+Shift+Y (macOS New Sticky Note service) #1007

From the post-merge audit of PRs #1003/#1005.

Problem

goal-loop-preview ships on Cmd+Shift+Y because check:keybindings found the in-app chord free. But macOS reserves ⇧⌘Y for the system "New Sticky Note" service, and the checker models only in-app owners (its own reservations list and command table) — the audit flagged the OS-level collision the tooling cannot see. In practice Electron usually receives the chord first, but on configurations where the service fires (or users trained to avoid the chord), the binding is fragile in a way no current check will catch.

Intended behavior

• Pick a chord with no macOS service association (verify against System Settings > Keyboard > Shortcuts > App Shortcuts/Services), rebind in defaults.ts, and update the Settings row text + feature reference that name Cmd+Shift+Y.
• Consider teaching check:keybindings a small OS-reservation list so this class of conflict fails the check instead of relying on human memory.

Acceptance criteria

• New chord bound and consistent everywhere it is named
• npm run check:keybindings clean