feat: add useTheme hook for theme management

[salaarkhan-dev]

Add useTheme Hook for Theme Management

Description

This PR introduces a new useTheme custom hook that provides a clean and type-safe way to manage themes in AdminJS applications. The hook is built with TypeScript and includes performance optimizations.

Changes

• Added useTheme hook with TypeScript support
• Implemented memoization for better performance
• Added comprehensive documentation
• Included TypeScript type definitions
• Added error handling and development warnings

Features

• Get current theme information
• Switch between available themes
• Check if a specific theme is active
• Access all available themes
• Full TypeScript support with proper type inference

Usage

import { useTheme } from 'adminjs'

function ThemeSwitcher() {
  const { theme, setTheme, availableThemes, isThemeActive } = useTheme()
  
  return (
    <select 
      value={theme?.id} 
      onChange={(e) => setTheme(e.target.value)}
    >
      {availableThemes.map(t => (
        <option key={t.id} value={t.id}>
          {t.name} {isThemeActive(t.id) && '(Active)'}
        </option>
      ))}
    </select>
  )
}