Fix/theme toggle button visible on all screen sizes(#1276)

[Jayant-1]

fix: add theme toggle button visible on all screen sizes

fixes #1276

1.Created a new [ThemeToggle]component in [theme-toggle.tsx] that:

• Is mobile-first with responsive design
• Persists theme preference in localStorage
• Respects system color scheme preference
• Is fully accessible with proper ARIA labels
• Has smooth hover transitions

2.Updated the layout in [layout.tsx] to:

• Position both theme toggle and locale switcher consistently
• Use fixed positioning for better visibility
• Add proper spacing and z-index

3.Features of the implementation:

• Supports both light and dark themes
• Includes smooth hover animations
• Preserves user preferences
• Works on all screen sizes
• Maintains consistent spacing with locale switcher