Extend availability (durations, weekly recurrence, calendar); price offerings in dollars

Availability (#2):
- us_availability gains offering_id, duration_minutes (default 60), and
  recurrence_group; AvailabilitySlot carries the new fields.
- AvailabilityRepository::createWeeklySeries() generates N weekly rows
  sharing a recurrence_group; findAvailable() filters by offering and
  duration. Date math uses DateTimeImmutable::modify() (the no-debug CI
  regex `dd\(` matches `->add(`).
- REST GET filters by offering_id/duration_minutes; POST accepts
  duration_minutes, offering_id, recurrence (single|weekly) + weeks.
- Admin form adds duration, an offering picker, and one-off/weekly options
  (OfferingRepository wired into AvailabilityController).
- booking.js renders an agenda calendar (slots grouped by day, with
  duration). The richer booking UX lands with the booking-flow work.

Offering price in dollars:
- Switch us_offerings.price_cents (INT) to price DECIMAL(10,2); Offering
  uses float $price. Admin form and REST take dollars.
- Fix a pre-existing misalignment in the Offering insert/update $wpdb
  format arrays (billing_mode/capacity/is_active were mapped to the wrong
  specifiers, which would corrupt values) via a single COLUMN_FORMATS list.

Also bump PHPStan to --memory-limit=1G in the lint script; 128M now
crashes analysis as the codebase has grown.

Refs #2

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

templates/admin/availability.php

@@ -5,7 +5,10 @@ if (! defined('ABSPATH')) {
     exit;
 }
 
-/** @var list<\Unsupervised\Schedular\Model\AvailabilitySlot> $slots */
+/**
+ * @var list<\Unsupervised\Schedular\Availability\AvailabilitySlot> $slots
+ * @var list<\Unsupervised\Schedular\Offering\Offering>             $offeringChoices
+ */
 ?>
 <div class="wrap">
     <h1><?php esc_html_e('My Availability', 'unsupervised-schedular'); ?></h1>
@@ -23,6 +26,35 @@ if (! defined('ABSPATH')) {
                 <th><label for="end_dt"><?php esc_html_e('End', 'unsupervised-schedular'); ?></label></th>
                 <td><input type="datetime-local" name="end_dt" id="end_dt" required></td>
             </tr>
+            <tr>
+                <th><label for="duration_minutes"><?php esc_html_e('Lesson length (minutes)', 'unsupervised-schedular'); ?></label></th>
+                <td>
+                    <select name="duration_minutes" id="duration_minutes">
+                        <option value="30">30</option>
+                        <option value="60" selected>60</option>
+                    </select>
+                </td>
+            </tr>
+            <tr>
+                <th><label for="offering_id"><?php esc_html_e('Offering', 'unsupervised-schedular'); ?></label></th>
+                <td>
+                    <select name="offering_id" id="offering_id">
+                        <option value="0"><?php esc_html_e('— Any private lesson —', 'unsupervised-schedular'); ?></option>
+                        <?php foreach ($offeringChoices as $offering) : ?>
+                            <option value="<?php echo esc_attr((string) $offering->id); ?>"><?php echo esc_html($offering->title); ?></option>
+                        <?php endforeach; ?>
+                    </select>
+                </td>
+            </tr>
+            <tr>
+                <th><?php esc_html_e('Repeat', 'unsupervised-schedular'); ?></th>
+                <td>
+                    <label><input type="radio" name="recurrence" value="single" checked> <?php esc_html_e('One-off', 'unsupervised-schedular'); ?></label>
+                    &nbsp;
+                    <label><input type="radio" name="recurrence" value="weekly"> <?php esc_html_e('Weekly for', 'unsupervised-schedular'); ?></label>
+                    <input type="number" name="weeks" min="1" max="52" value="12" style="width:5em;"> <?php esc_html_e('weeks', 'unsupervised-schedular'); ?>
+                </td>
+            </tr>
         </table>
         <?php submit_button(esc_html__('Add Slot', 'unsupervised-schedular')); ?>
     </form>
@@ -37,6 +69,7 @@ if (! defined('ABSPATH')) {
                 <tr>
                     <th><?php esc_html_e('Start', 'unsupervised-schedular'); ?></th>
                     <th><?php esc_html_e('End', 'unsupervised-schedular'); ?></th>
+                    <th><?php esc_html_e('Length', 'unsupervised-schedular'); ?></th>
                     <th><?php esc_html_e('Status', 'unsupervised-schedular'); ?></th>
                     <th><?php esc_html_e('Actions', 'unsupervised-schedular'); ?></th>
                 </tr>
@@ -46,6 +79,7 @@ if (! defined('ABSPATH')) {
                     <tr>
                         <td><?php echo esc_html($slot->startDt); ?></td>
                         <td><?php echo esc_html($slot->endDt); ?></td>
+                        <td><?php echo esc_html((string) $slot->durationMinutes . ' min'); ?></td>
                         <td><?php echo $slot->isBooked ? esc_html__('Booked', 'unsupervised-schedular') : esc_html__('Available', 'unsupervised-schedular'); ?></td>
                         <td>
                             <?php if (! $slot->isBooked) : ?>