Standardize the ATET header appearance menu

[0thernet]

Summary

• replace the footer Light/Dark/System tabs with one shared icon menu as the final header action on the homepage and 404
• consume the immutable framework-neutral design-kit v0.1.8 browser runtime and preserve the existing atet.appearance preference
• keep first paint and browser chrome synchronized with System or explicit saved preferences
• pin Bun type definitions in package smoke to the repository-required Bun 1.3.14 contract

Validation

• bun run check
• apps/web bun run check
• isolated apps/web frozen install
• Chromium: opposing OS/saved preferences, keyboard selection, focus, one final header control, 404 narrow layout, and 48px coarse-pointer target

[vercel]

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Project	Deployment	Actions	Updated (UTC)
atet	Ready	Preview	Aug 21, 2026 4:56pm