Omit the class description when the group block shows one class

The Group Classes block can be pinned to a single class via its Class
option so it can be embedded on a page dedicated to that class. On such a
page the surrounding copy already describes the class, so the card
repeated it. In single-class mode the description is now left out and the
card shows only the schedule, instructor, schedule note, price, enrolment
deadline and the enrol/withdraw controls.

The editor preview follows the same rule: BlockPreview::groupClasses()
takes the mode from the block's offeringId attribute, drops the sample
description when a class is pinned, and notes what the published page
shows. Its sample card also gained the .us-class-when and
.us-enrol-deadline elements the live markup has always rendered.

Closes #114

Co-Authored-By: Claude Opus 5 <[email protected]>

assets/js/group-classes.js

@@ -12,6 +12,9 @@
 
     // When the shortcode/block pins a single offering, only that class is
     // shown, so the page can be embedded alongside a full class description.
+    // The class's own description is then omitted from the card — the page it
+    // sits on already describes the class — leaving the schedule, price and
+    // enrolment controls.
     const singleOfferingId = Number(app.dataset.offering || 0);
 
     function apiFetch(path, options = {}) {
@@ -148,7 +151,7 @@
                 ${whenLabel(o) ? `<p class="us-class-when">${escHtml(whenLabel(o))}</p>` : ''}
                 ${o.instructor_name ? `<p class="us-class-instructor">With ${escHtml(o.instructor_name)}</p>` : ''}
                 ${o.schedule_note ? `<p>${escHtml(o.schedule_note)}</p>` : ''}
-                ${o.description ? `<p>${escHtml(o.description)}</p>` : ''}
+                ${!singleOfferingId && o.description ? `<p>${escHtml(o.description)}</p>` : ''}
                 <p>${escHtml(Number(o.price).toFixed(2))} ${escHtml(o.currency)}</p>
                 ${!enrolledMap.has(Number(o.id)) && isEnrollmentOpen(o) && enrolmentDeadline(o)
         ? `<p class="us-enrol-deadline">Enrol by ${escHtml(formatDate(enrolmentDeadline(o)))}</p>`