[feature]: Add loading="lazy" to testimonial images for better performance

### Is there an existing feature request for this?

- [x] I have searched the existing issues

### Summary

## 🐢 Problem
Testimonial images in `index.html` (`.avif` and `.jpg` files) are loaded eagerly on page load. This means all 5 testimonial profile pictures are downloaded immediately, even before the user scrolls to the testimonials section — wasting bandwidth and slowing initial page load.

## ✅ Suggested Fix
Add the native HTML `loading="lazy"` attribute to all testimonial `` tags in `index.html`.

**File:** `index.html`

**Current code (example):**
```html





```

**Fix:**
```html





```

### Why should this be worked on?

## 🎯 Benefits
- ⚡ Faster initial page load
- 📉 Reduced bandwidth usage
- 📱 Better experience on mobile and slow networks
- ♿ Bonus: fixing `alt=""` improves accessibility too

## 🌐 Browser Support
`loading="lazy"` is supported in all modern browsers (Chrome, Firefox, Edge, Safari 15.4+). No polyfill needed.

Open index.html and locate the five testimonial image tags under images/testimonials. Add lazy loading to each testimonial image, then inspect the page or search the file to confirm all five use loading="lazy" and no testimonial image was missed.

Written by the indexing model from the issue text.