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>

src/Offering/OfferingRepository.php

@@ -11,11 +11,20 @@ class OfferingRepository {
 		$this->table = $db->prefix . 'us_offerings';
 	}
 
+	/**
+	 * Column formats aligned to {@see columns()} (instructor_id, kind, title,
+	 * description, duration_minutes, price, currency, billing_mode, allow_weekly,
+	 * capacity, term_start, term_end, schedule_note, is_active).
+	 *
+	 * @var list<string>
+	 */
+	private const COLUMN_FORMATS = [ '%d', '%s', '%s', '%s', '%d', '%f', '%s', '%s', '%d', '%d', '%s', '%s', '%s', '%d' ];
+
 	public function insert( Offering $offering ): int {
 		$this->db->insert(
 			$this->table,
 			$this->columns( $offering ) + [ 'created_at' => current_time( 'mysql' ) ],
-			[ '%d', '%s', '%s', '%s', '%d', '%s', '%s', '%d', '%d', '%s', '%s', '%s', '%d', '%s' ]
+			[ ...self::COLUMN_FORMATS, '%s' ]
 		);
 
 		return $this->db->insert_id;
@@ -26,7 +35,7 @@ class OfferingRepository {
 			$this->table,
 			$this->columns( $offering ),
 			[ 'id' => $id ],
-			[ '%d', '%s', '%s', '%s', '%d', '%s', '%s', '%d', '%d', '%s', '%s', '%s', '%d' ],
+			self::COLUMN_FORMATS,
 			[ '%d' ]
 		);
 	}
@@ -43,7 +52,7 @@ class OfferingRepository {
 			'title'            => $offering->title,
 			'description'      => $offering->description,
 			'duration_minutes' => $offering->durationMinutes,
-			'price_cents'      => $offering->priceCents,
+			'price'            => $offering->price,
 			'currency'         => $offering->currency,
 			'billing_mode'     => $offering->billingMode,
 			'allow_weekly'     => $offering->allowWeekly ? 1 : 0,