Fix mobile Slot menu access

[woahitsraj]

Summary

• keep the first Slot tap focus-only, then open the Slot Menu when the focused Slot is tapped again
• disable double-tap zoom on Slots while preserving normal touch scrolling and pinch zoom
• extend Edge Menu backdrops through safe-area gutters while keeping Menu panels inside the Safe Canvas
• add touch-enabled WebKit coverage for selection, Menu commands, Close, backdrop dismissal, and Move

Verification

• pnpm lint
• pnpm typecheck
• pnpm test:unit -- --run
• targeted Chromium and iPhone WebKit Playwright coverage for Slot taps and Menu touch controls
• portrait and landscape Playwright coverage for full-viewport Menu backdrops