Add Worlds page and nav link; first world: Delph Woods

- worlds.html: new page matching videos.html style, grid of world cards
  with illustrated preview thumbnails and Explore links
- World card CSS added to style.css (.world-card, .world-card-preview,
  .world-enter)
- Delph Woods card links to worlds/delphwoods.html with a woodland SVG
  preview, description, and location/3DGS chips
- Worlds added to nav and footer Product column on all 5 existing pages
- CTA band on worlds page promotes consultancy for commissioning

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

style.css

@@ -857,6 +857,52 @@ img { display: block; max-width: 100%; }
   margin-top: 8px;
 }
 
+/* ── World cards ─────────────────────────────── */
+.world-card {
+  display: block;
+  text-decoration: none;
+  color: inherit;
+}
+
+.world-card-preview {
+  position: relative;
+  border-radius: 16px;
+  overflow: hidden;
+  height: 220px;
+  background: #0E1A12;
+  transition: opacity 0.18s;
+}
+
+.world-card:hover .world-card-preview { opacity: 0.88; }
+
+.world-enter {
+  position: absolute;
+  bottom: 14px;
+  right: 14px;
+  background: rgba(255,255,255,0.92);
+  color: #0A0A0A;
+  font-family: var(--mono);
+  font-size: 12px;
+  font-weight: 600;
+  letter-spacing: 0.06em;
+  padding: 7px 13px;
+  border-radius: 999px;
+}
+
+.world-card-title {
+  font-size: 16px;
+  font-weight: 600;
+  letter-spacing: -0.01em;
+  margin-top: 14px;
+  margin-bottom: 4px;
+}
+
+.world-card-desc {
+  font-size: 14px;
+  color: var(--ink-3);
+  line-height: 1.5;
+}
+
 /* ── Section sub-header ──────────────────────── */
 .section-sub-header {
   display: flex;