[codex] Warm Fold design system rollout

[lsdragst-a11y]

Summary

• Add the Warm Fold homepage design specification and P0 foundation docs.
• Implement Warm Fold tokens, font variables, SVG brand assets, BrandMark, and primitive UI components.
• Apply Warm Fold to auth pages, homepage, notebook library, note workspace shell, and shared navigation.
• Add CI checks for Warm Fold asset validation and Next.js production build.

Validation

• npm run validate:warm-fold
• npm test
• npx tsc --noEmit --pretty false
• npm run build
• Scoped ESLint checks for touched pages/components

Known Baseline

• Full ESLint still reports existing errors in ChatPanel.tsx and lib/progress.ts; these were left out of scope.