{Feature}: Add Export Options (PNG, JPEG, WebP) And Download Quality Slider

🔧 Description
This PR #138
adds export functionality to the Meme Generator, allowing users to:
- Download memes in multiple formats: PNG, JPEG, WebP
- Adjust download quality for JPEG/WebP using a slider
- Minor frontend improvements for a cleaner UI

🧩 Changes Made
- Export dropdown with file type selection
- Quality slider with dynamic preview
- Updated download logic for multiple formats

💡 How to Test
1. Create a meme
2. Choose format from dropdown
3. Adjust quality slider
4. Click "Download" — image should save correctly

🏷️ Notes
- Compatible with modern browsers
- Tested locally with different formats and qualities
- Hacktoberfest contribution 🎃

✅ Checklist
- [x] Feature implemented
- [x] UI tested locally
- [x] No breaking changes
- [x] Ready for review

🌸 Hacktoberfest 2025
Contribution made as part of Hacktoberfest 2025 — happy to support open-source!