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]>

templates/admin/group-classes.php

@@ -5,29 +5,56 @@ if (! defined('ABSPATH')) {
     exit;
 }
 
-/** @var list<array{student: string, offering: string, status: string}> $rows */
+/**
+ * @var list<array{id: int|null, title: string, instructor: string, when: string, capacity: int|null, enrolled: int, invite_only: bool}> $rows
+ * @var string $notice
+ * @var string $baseUrl
+ */
 ?>
 <div class="wrap">
     <h1><?php esc_html_e('Group Classes', 'unsupervised-schedular'); ?></h1>
-    <p class="description"><?php esc_html_e('Active enrolments across all group classes.', 'unsupervised-schedular'); ?></p>
+    <p class="description"><?php esc_html_e('Every group class across instructors. Select one for its details, roster, and — for invite-only classes — to invite or add students.', 'unsupervised-schedular'); ?></p>
+
+    <?php if ('' !== $notice) : ?>
+        <div class="notice notice-info is-dismissible"><p><?php echo esc_html($notice); ?></p></div>
+    <?php endif; ?>
 
     <?php if (empty($rows)) : ?>
-        <p><?php esc_html_e('No active enrolments.', 'unsupervised-schedular'); ?></p>
+        <p><?php esc_html_e('No group classes.', 'unsupervised-schedular'); ?></p>
     <?php else : ?>
         <table class="wp-list-table widefat fixed striped">
             <thead>
                 <tr>
-                    <th><?php esc_html_e('Student', 'unsupervised-schedular'); ?></th>
                     <th><?php esc_html_e('Class', 'unsupervised-schedular'); ?></th>
-                    <th><?php esc_html_e('Status', 'unsupervised-schedular'); ?></th>
+                    <th><?php esc_html_e('Instructor', 'unsupervised-schedular'); ?></th>
+                    <th><?php esc_html_e('When', 'unsupervised-schedular'); ?></th>
+                    <th><?php esc_html_e('Enrolled', 'unsupervised-schedular'); ?></th>
+                    <th><?php esc_html_e('Actions', 'unsupervised-schedular'); ?></th>
                 </tr>
             </thead>
             <tbody>
                 <?php foreach ($rows as $row) : ?>
                     <tr>
-                        <td><?php echo esc_html($row['student']); ?></td>
-                        <td><?php echo esc_html($row['offering']); ?></td>
-                        <td><?php echo esc_html($row['status']); ?></td>
+                        <td>
+                            <?php echo esc_html($row['title']); ?>
+                            <?php if ($row['invite_only']) : ?>
+                                <span class="dashicons dashicons-lock" title="<?php esc_attr_e('Invite only', 'unsupervised-schedular'); ?>"></span>
+                            <?php endif; ?>
+                        </td>
+                        <td><?php echo esc_html($row['instructor']); ?></td>
+                        <td><?php echo '' !== $row['when'] ? esc_html($row['when']) : '&mdash;'; ?></td>
+                        <td>
+                            <?php
+                            if (null === $row['capacity']) {
+                                echo esc_html((string) $row['enrolled']);
+                            } else {
+                                echo esc_html($row['enrolled'] . ' / ' . $row['capacity']);
+                            }
+                            ?>
+                        </td>
+                        <td>
+                            <a class="button button-small" href="<?php echo esc_url(add_query_arg('class_id', (int) $row['id'], $baseUrl)); ?>"><?php echo $row['invite_only'] ? esc_html__('View & invite', 'unsupervised-schedular') : esc_html__('View details', 'unsupervised-schedular'); ?></a>
+                        </td>
                     </tr>
                 <?php endforeach; ?>
             </tbody>