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 <[email protected]>

src/Offering/Offering.php

@@ -29,7 +29,7 @@ class Offering {
 		public readonly int $instructorId,
 		public readonly string $kind,
 		public readonly string $title,
-		public readonly int $priceCents = 0,
+		public readonly float $price = 0.0,
 		public readonly string $currency = 'CAD',
 		public readonly string $billingMode = self::BILLING_ONE_TIME,
 		public readonly ?string $description = null,
@@ -48,7 +48,7 @@ class Offering {
 			instructorId:    (int) $row->instructor_id,
 			kind:            $row->kind,
 			title:           $row->title,
-			priceCents:      (int) $row->price_cents,
+			price:           (float) $row->price,
 			currency:        $row->currency,
 			billingMode:     $row->billing_mode,
 			description:     $row->description,
@@ -76,7 +76,7 @@ class Offering {
 			'title'            => $this->title,
 			'description'      => $this->description,
 			'duration_minutes' => $this->durationMinutes,
-			'price_cents'      => $this->priceCents,
+			'price'            => $this->price,
 			'currency'         => $this->currency,
 			'billing_mode'     => $this->billingMode,
 			'allow_weekly'     => $this->allowWeekly,