feat: implement dark mode toggle functionality with theme persistence

[nazneen-p1]

📝 Pull Request Description

Related Issue

Closes #532

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Summary

This PR implements a dark mode toggle feature for the application. Users can switch between light and dark themes using a toggle button, and the selected theme is persisted using local storage.

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Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New project addition
• 🚀 New feature or UI/UX enhancement
• ♻️ Code refactoring / clean-up
• 📝 Documentation update
• ⚙️ GitHub Workflow automation or DX improvements

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🛠️ Changes Made

• Added dark mode toggle button functionality
• Implemented theme switching using data-theme attribute
• Used CSS variables for light and dark theme styling
• Stored user preference in local storage for persistence
• Ensured theme is restored on page reload

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🧪 Testing and Verification

Local Validation

• Verified toggle button switches theme correctly
• Verified theme persists after page reload

Browser Compatibility Check

• Tested and verified in Google Chrome
• Tested and verified in Mozilla Firefox
• Tested and verified in Safari / Microsoft Edge

Responsive & Accessibility Checks

• Verified responsive layout on Mobile viewports
• Verified responsive layout on Tablet viewports
• Keyboard navigation and focus outlines checked
• Semantic HTML and ARIA labels checked

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📷 Screenshots / Video Recording

Dark mode toggle button successfully switches between light and dark themes with persistent user preference.

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🤝 Contributor Checklist

• My code follows the code style guidelines of this project.
• I have performed a self-review of my own code.
• My changes generate no new warnings or console errors.
• There are no unrelated changes or formatter noise in this PR.
• I have updated the documentation / README files accordingly.

[nazneen-p1]

Hi @PatelHarsh2006,

I have completed the implementation for this issue and created a PR.
Could you please review it and consider merging if everything looks good?

Thank you!