[NSoC'26] Add JSON/CSV export and offline caching support

[Aishwarya-Anekar]

🔁 Pull Request

[NSoC'26] Add JSON/CSV export and offline caching support

📌 Description

Implemented export functionality for periodic table and trends data along with improved offline usability.

Added Features

• JSON export support
• CSV export support
• Export buttons in Trends and Element Details sections
• Lightweight offline caching using a service worker

These improvements allow users to save, reuse, and access important data even with limited internet connectivity.

🔗 Related Issue

Fixes #93

🚀 Type of Change

• [✅] Bug Fix
• [✅] Feature
• [✅] Enhancement
• [✅] Documentation

🧪 Testing

Tested locally by:

• Exporting data in JSON format
• Exporting data in CSV format
• Verifying downloaded file contents
• Testing Trends and Element Details export buttons
• Checking offline behavior after service worker caching
• Ensuring existing UI functionality remains unaffected

📸 Screenshots

Periodic.Table.Explorer.-.Google.Chrome.2026-05-21.01-30-41.mp4

✅ Checklist

• [✅] Code follows guidelines
• [✅] Tested properly
• [✅] Docs updated
• [✅] PR title includes NSoC'26

🌱 NSoC'26 Rule

All PRs must include NSoC'26 in the title.

Example:
[NSoC'26] Add authentication system