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>

tests/Unit/Offering/OfferingTest.php

@@ -14,7 +14,7 @@ class OfferingTest extends TestCase
             instructorId:    5,
             kind:            Offering::KIND_PRIVATE_LESSON,
             title:           '30-min Piano',
-            priceCents:      3500,
+            price:           35.00,
             billingMode:     Offering::BILLING_ONE_TIME,
             durationMinutes: 30,
             id:              42,
@@ -23,7 +23,7 @@ class OfferingTest extends TestCase
         self::assertSame(5, $offering->instructorId);
         self::assertSame(Offering::KIND_PRIVATE_LESSON, $offering->kind);
         self::assertSame('30-min Piano', $offering->title);
-        self::assertSame(3500, $offering->priceCents);
+        self::assertSame(35.00, $offering->price);
         self::assertSame(30, $offering->durationMinutes);
         self::assertSame(42, $offering->id);
     }
@@ -32,7 +32,7 @@ class OfferingTest extends TestCase
     {
         $offering = new Offering(1, Offering::KIND_GROUP_CLASS, 'Choir');
 
-        self::assertSame(0, $offering->priceCents);
+        self::assertSame(0.0, $offering->price);
         self::assertSame('CAD', $offering->currency);
         self::assertSame(Offering::BILLING_ONE_TIME, $offering->billingMode);
         self::assertNull($offering->durationMinutes);
@@ -51,7 +51,7 @@ class OfferingTest extends TestCase
             'title'            => 'Year Choir',
             'description'      => 'Weekly choir',
             'duration_minutes' => null,
-            'price_cents'      => '12000',
+            'price'            => '120.00',
             'currency'         => 'CAD',
             'billing_mode'     => Offering::BILLING_FULL_TERM,
             'allow_weekly'     => '0',
@@ -67,7 +67,7 @@ class OfferingTest extends TestCase
         self::assertSame(7, $offering->id);
         self::assertSame(3, $offering->instructorId);
         self::assertNull($offering->durationMinutes);
-        self::assertSame(12000, $offering->priceCents);
+        self::assertSame(120.00, $offering->price);
         self::assertSame(20, $offering->capacity);
         self::assertSame(Offering::BILLING_FULL_TERM, $offering->billingMode);
         self::assertTrue($offering->isActive);
@@ -78,7 +78,7 @@ class OfferingTest extends TestCase
         $offering = new Offering(1, Offering::KIND_PRIVATE_LESSON, 'Lesson', id: 10);
         $arr      = $offering->toArray();
 
-        foreach (['id', 'instructor_id', 'kind', 'title', 'price_cents', 'billing_mode', 'is_active'] as $key) {
+        foreach (['id', 'instructor_id', 'kind', 'title', 'price', 'billing_mode', 'is_active'] as $key) {
             self::assertArrayHasKey($key, $arr);
         }
     }