Fix clipped dashboard tooltips

[ael-dev3]

Summary

• render explanatory tooltips in a viewport-level portal
• flip and clamp against the visual viewport and Farcaster safe areas
• synchronize hover, focus, touch, Escape, outside-click, and ARIA behavior
• add mobile geometry and interaction regressions, including 320px asymmetric insets

Validation

• pnpm lint
• pnpm typecheck
• pnpm test (229 tests)
• pnpm build
• pnpm test:e2e (8 tests)
• pnpm security:check
• independent no-blocker review