Integrate 2026 UI design system

[LetsPaddock]

Summary

• Integrates the 2026 DAEMON UI foundation: near-monochrome stone tokens, sharp shell panes, small-radius controls, hairline panel structure, and self-hosted Geist Mono.
• Adds first-class light theme support via data-theme="light" with a Settings display toggle.
• Updates core shell/overlay primitives, onboarding/confirm flows, command palette/drawer, editor/terminal theme constants, and design-system docs.
• Routes Settings/titlebar/sidebar bridge calls through the safe daemon bridge for browser preview resilience.

Verification

• pnpm run typecheck
• pnpm run lint:styles
• pnpm run build
• pnpm run test:ui
• Browser preview: verified dark shell, narrow Settings layout, and light theme toggle