Add group-class scheduling, instructor assignment, and details/invite management

Group classes now carry a specific class time (alongside date and duration)
and an assigned instructor:

- Schema: add `class_time` (TIME) to `us_offerings`; `Offering` gains
  `normalizeTime`/`sessionWindows`. (Rides the pending 1.0.0->1.1.0 dbDelta
  upgrade, so no version bump.)
- Offering form: class-time field, plus a studio-admin instructor picker
  (plain instructors always own their own classes).
- `ClassSlotReconciler`: assigning an instructor clears their open booking
  slots overlapping each session and flags already-booked lessons that clash
  (a booked lesson is never deleted). Uses new
  `AvailabilityRepository::findOverlapping`.
- Front end: `GET /offerings` exposes `instructor_name`; the enrolment page
  shows who teaches each class and when it meets.

Back-office group-class views redesigned:

- Instructor **My Group Classes** and studio-admin **Group Classes** are now
  per-class summaries with enrolment counts, not flat student lists.
- Each links through (`?class_id=<id>`) to a per-class **details page**
  (schedule panel, roster with payment status, and — for invite-only classes
  — the add/make-available/invite-by-email controls). Invite-only membership
  is managed entirely from this page.
- Invite actions are allowed for the class's owning instructor or any
  `view_all_lessons` studio admin, so an owner-operator (studio admin who also
  teaches) can reach every class's roster and invites from the Group Classes
  page.

Tests: composer test (508), composer lint, composer cs all pass.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

assets/js/group-classes.js

@@ -89,6 +89,20 @@
         return `${formatDate(o.term_start)} – ${formatDate(o.term_end)} (${sessions} weekly sessions)`;
     }
 
+    // Format a stored H:i(:s) class time as a friendly local-clock label.
+    function timeLabel(o) {
+        if (!o.class_time) return '';
+        const [h, m] = o.class_time.split(':').map(Number);
+        const d = new Date();
+        d.setHours(h, m, 0, 0);
+        return d.toLocaleTimeString(undefined, { hour: 'numeric', minute: '2-digit' });
+    }
+
+    // The "when" line combines the date (or date range) with the class time.
+    function whenLabel(o) {
+        return [termLabel(o), timeLabel(o)].filter(Boolean).join(' · ');
+    }
+
     function renderClasses(offerings, enrolledOfferingIds) {
         let groups = offerings.filter((o) => o.kind === 'group_class');
         if (singleOfferingId) {
@@ -104,7 +118,8 @@
         list.innerHTML = groups.map((o) => `
             <div class="us-class">
                 <h3>${escHtml(o.title)}</h3>
-                ${termLabel(o) ? `<p>${escHtml(termLabel(o))}</p>` : ''}
+                ${whenLabel(o) ? `<p class="us-class-when">${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>` : ''}
                 <p>${escHtml(Number(o.price).toFixed(2))} ${escHtml(o.currency)}</p>