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/offerings.php

@@ -10,6 +10,9 @@ if (! defined('ABSPATH')) {
 /**
  * @var list<\Unsupervised\Schedular\Offering\Offering> $offerings
  * @var \Unsupervised\Schedular\Offering\Offering|null  $editing  Offering loaded into the form, or null when adding.
+ * @var list<array{id: int, name: string}>              $instructors  Instructors offered in the assignment picker (studio admins only).
+ * @var bool                                            $manageAll  Whether the current user may assign classes to other instructors.
+ * @var string                                          $notice  Status message from the last save (slot-clearing / conflicts).
  */
 
 $baseUrl = admin_url('admin.php?page=us-offerings');
@@ -26,6 +29,10 @@ if ($editing && null !== $editing->termStart && null !== $editing->termEnd && $e
 <div class="wrap">
     <h1><?php esc_html_e('Offerings', 'unsupervised-schedular'); ?></h1>
 
+    <?php if ('' !== $notice) : ?>
+        <div class="notice notice-info is-dismissible"><p><?php echo esc_html($notice); ?></p></div>
+    <?php endif; ?>
+
     <h2><?php $editing ? esc_html_e('Edit Offering', 'unsupervised-schedular') : esc_html_e('Add Offering', 'unsupervised-schedular'); ?></h2>
     <form method="post">
         <?php wp_nonce_field('usc_offering_action'); ?>
@@ -49,6 +56,19 @@ if ($editing && null !== $editing->termStart && null !== $editing->termEnd && $e
                     </select>
                 </td>
             </tr>
+            <?php if ($manageAll) : ?>
+                <tr>
+                    <th><label for="class_instructor_id"><?php esc_html_e('Instructor', 'unsupervised-schedular'); ?></label></th>
+                    <td>
+                        <select name="class_instructor_id" id="class_instructor_id">
+                            <?php foreach ($instructors as $instructor) : ?>
+                                <option value="<?php echo esc_attr((string) $instructor['id']); ?>" <?php echo $editing && $editing->instructorId === $instructor['id'] ? 'selected' : ''; ?>><?php echo esc_html($instructor['name']); ?></option>
+                            <?php endforeach; ?>
+                        </select>
+                        <p class="description"><?php esc_html_e('Who teaches this. Assigning a group class clears that instructor’s open booking slots at the class time.', 'unsupervised-schedular'); ?></p>
+                    </td>
+                </tr>
+            <?php endif; ?>
             <tr>
                 <th><label for="description"><?php esc_html_e('Description', 'unsupervised-schedular'); ?></label></th>
                 <td><textarea name="description" id="description" class="large-text" rows="4"><?php echo esc_textarea($editing->description ?? ''); ?></textarea></td>
@@ -85,6 +105,13 @@ if ($editing && null !== $editing->termStart && null !== $editing->termEnd && $e
                     <span class="description"><?php esc_html_e('Group classes only — date of the first class', 'unsupervised-schedular'); ?></span>
                 </td>
             </tr>
+            <tr>
+                <th><label for="class_time"><?php esc_html_e('Class time', 'unsupervised-schedular'); ?></label></th>
+                <td>
+                    <input type="time" name="class_time" id="class_time" value="<?php echo esc_attr(null === ($editing->classTime ?? null) ? '' : substr((string) $editing->classTime, 0, 5)); ?>">
+                    <span class="description"><?php esc_html_e('Group classes only — the time each session starts. Combined with the duration to block the instructor’s availability.', 'unsupervised-schedular'); ?></span>
+                </td>
+            </tr>
             <tr>
                 <th><?php esc_html_e('Sessions', 'unsupervised-schedular'); ?></th>
                 <td>
@@ -164,10 +191,17 @@ if ($editing && null !== $editing->termStart && null !== $editing->termEnd && $e
                         <td>
                             <?php if (null === $offering->termStart) : ?>
                                 &mdash;
-                            <?php elseif (null === $offering->termEnd || $offering->termEnd === $offering->termStart) : ?>
-                                <?php echo esc_html((string) mysql2date('M j, Y', $offering->termStart)); ?>
                             <?php else : ?>
-                                <?php echo esc_html((string) mysql2date('M j, Y', $offering->termStart) . ' – ' . (string) mysql2date('M j, Y', $offering->termEnd)); ?>
+                                <?php
+                                if (null === $offering->termEnd || $offering->termEnd === $offering->termStart) {
+                                    echo esc_html((string) mysql2date('M j, Y', $offering->termStart));
+                                } else {
+                                    echo esc_html((string) mysql2date('M j, Y', $offering->termStart) . ' – ' . (string) mysql2date('M j, Y', $offering->termEnd));
+                                }
+                                if (null !== $offering->classTime) {
+                                    echo '<br><span class="description">' . esc_html((string) mysql2date('g:i a', $offering->termStart . ' ' . $offering->classTime)) . '</span>';
+                                }
+                                ?>
                             <?php endif; ?>
                         </td>
                         <td><?php echo $offering->isActive ? esc_html__('Yes', 'unsupervised-schedular') : esc_html__('No', 'unsupervised-schedular'); ?></td>