[area:shadcn] header & sidebar — swap navbar/btn-ghost to shadcn Button

[fray-cloud]

Scope

• apps/web/src/new-component/header/**
• any shared sidebar/nav component referenced by Header
• daisyUI classes touched: navbar, btn, btn-ghost

Acceptance

• npx nx affected -t lint test build green
• Header source contains zero daisyUI classes (grep clean in touched files)
• No btn + Button mixed usage inside any touched file
• Visual parity verified manually on nx serve web
• daisyUI plugin still enabled globally (other pages still use it)

Depends on

• [area:shadcn] add button, card, skeleton, avatar, progress components #49

Research

• context7: shadcn Button variants
• fallback: https://ui.shadcn.com/docs/components/button

Risk

med — header is on every page; visual regressions are user-visible.

Steps

1. Replace navbar layout with a flex container composed of shadcn Button + lucide-react icons.
2. Map btn-ghost → <Button variant="ghost">; map plain btn → <Button>.
3. Keep existing routing Link behavior via shadcn Button asChild.
4. Remove all daisyUI classes from touched files.
5. npx nx affected -t lint test build.

[fray-cloud]

Landed in dev via #61 (rebase merge).