(SP: 2) [Frontend] Remove [locale] layout force-dynamic and move auth to client-side #369
Description
Summary
Remove auth/cookie access from `app/[locale]/layout.tsx` so public locale pages can use static/ISR rendering.
Scope
- Update `/api/auth/me` to return lightweight auth payload and no-store
- Add `useAuth` + `AuthProvider`
- Move header auth consumption to client hook
- Keep dashboard explicitly dynamic via `app/[locale]/dashboard/layout.tsx`
Acceptance Criteria
- `app/[locale]/layout.tsx` has no `getCurrentUser()` and no `force-dynamic`
- Header auth state is loaded via client API
- Dashboard remains dynamic (`force-dynamic`)
- Target files pass lint