feat(navigation): Dropdown Menu with keyboard navigation and animations

[KeenIsHere]

Overview

This issue proposes adding a Dropdown Menu component to the navigation category of Animata.

A dropdown menu is one of the most commonly needed UI patterns in SaaS and web applications. Animata currently has no navigation dropdown — this fills that gap with a fully accessible, animated, copy-paste-ready component.

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Component Details

File: animata/navigation/dropdown-menu.tsx
Category: Navigation
Type: Interactive component

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Proposed Features

• Trigger button that opens and closes a dropdown panel below it
• Menu items with optional icon and label support
• Smooth open/close animation using framer-motion (opacity + translateY only)
• Keyboard navigation: Arrow Up/Down to move, Enter to select, Escape to close
• Click outside to close using a ref and useEffect mousedown listener
• Focus management: returns focus to trigger on Escape
• Fully accessible: aria-expanded, aria-haspopup, role="menu", role="menuitem"
• prefers-reduced-motion: animations disabled when user preference is set
• Mobile ready: tap to open and close
• Left and right alignment support via prop

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Props API

interface MenuItem {
  label: string;
  icon?: React.ReactNode;
  onClick?: () => void;
}

interface DropdownMenuProps {
  items?: MenuItem[];
  triggerLabel?: string;
  align?: "left" | "right";
}