Add image lightbox — click gallery image to view full-screen

Clicking any image in a post modal opens it full-screen with a dark
overlay. Close by clicking outside, the ✕ button, or pressing Escape.
Added zoom-in cursor and hover opacity to signal clickability.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

script.js

@@ -283,7 +283,7 @@ async function openPost(id) {
   }
 
   const galleryHTML = p.images?.length
-    ? `<div class="img-gallery">${p.images.map(src => `<img src="${src}" alt="${p.title}" />`).join('')}</div>`
+    ? `<div class="img-gallery">${p.images.map(src => `<img src="${src}" alt="${p.title}" onclick="openLightbox(this.src)" />`).join('')}</div>`
     : '';
 
   document.getElementById('modalContent').innerHTML = `
@@ -380,6 +380,21 @@ function closeModal() {
   document.body.style.overflow = '';
 }
 
+// ===========================
+// LIGHTBOX
+// ===========================
+function openLightbox(src) {
+  document.getElementById('lightboxImg').src = src;
+  document.getElementById('lightboxOverlay').classList.add('open');
+}
+function closeLightbox() {
+  document.getElementById('lightboxOverlay').classList.remove('open');
+  document.getElementById('lightboxImg').src = '';
+}
+document.addEventListener('keydown', e => {
+  if (e.key === 'Escape') closeLightbox();
+});
+
 document.addEventListener('keydown', e => { if (e.key === 'Escape') closeModal(); });
 
 // ===========================