small auth additions and some nav fixes

app/(content)/layout.tsx

app/api/signup/route.ts

app/globals.css

components/icons.tsx

components/mode-toggle.tsx

components/nav.tsx

components/search-input.tsx

components/site-footer.tsx

components/ui/button.tsx

lib/auth.ts

package-lock.json

package.json

prisma/schema.prisma

types/next-auth.d.ts