Add responsive navigation bar with mobile menu

[Muneerali199]

Summary

Create a sticky, responsive navbar with the Windmill logo, navigation links, and a mobile hamburger menu.

Tasks

• Create components/navbar.tsx with:
  • Sticky top positioning with blur backdrop
  • Logo/brand link
  • Nav links: Home, Dashboard, About
  • Mobile hamburger menu with slide-in panel
  • Active link highlighting
• Add navbar to layout.tsx
• Animate mobile menu open/close with framer-motion

Files to change

• components/navbar.tsx (new, ~150 lines)
• app/layout.tsx (~5 lines added)
• components/mobile-menu.tsx (new, ~80 lines)

Acceptance criteria

• Navbar appears on all pages
• Mobile menu works on small screens
• npm run build succeeds