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/OfferingEndpoint.php

@@ -85,7 +85,7 @@ class OfferingEndpoint {
 			instructorId:    get_current_user_id(),
 			kind:            $kind,
 			title:           $title,
-			priceCents:      absint( $request->get_param( 'price_cents' ) ),
+			price:           $this->price( $request->get_param( 'price' ) ),
 			currency:        sanitize_text_field( (string) ( $request->get_param( 'currency' ) ?? 'CAD' ) ),
 			billingMode:     $billingMode,
 			description:     $this->nullableText( $request->get_param( 'description' ) ),
@@ -129,7 +129,7 @@ class OfferingEndpoint {
 			instructorId:    $existing->instructorId,
 			kind:            $kind,
 			title:           $request->has_param( 'title' ) ? sanitize_text_field( (string) $request->get_param( 'title' ) ) : $existing->title,
-			priceCents:      $request->has_param( 'price_cents' ) ? absint( $request->get_param( 'price_cents' ) ) : $existing->priceCents,
+			price:           $request->has_param( 'price' ) ? $this->price( $request->get_param( 'price' ) ) : $existing->price,
 			currency:        $request->has_param( 'currency' ) ? sanitize_text_field( (string) $request->get_param( 'currency' ) ) : $existing->currency,
 			billingMode:     $billingMode,
 			description:     $request->has_param( 'description' ) ? $this->nullableText( $request->get_param( 'description' ) ) : $existing->description,
@@ -182,6 +182,10 @@ class OfferingEndpoint {
 		return new \WP_Error( 'invalid_offering', $message, [ 'status' => 400 ] );
 	}
 
+	private function price( mixed $value ): float {
+		return max( 0.0, (float) $value );
+	}
+
 	private function nullableInt( mixed $value ): ?int {
 		return ( null === $value || '' === $value ) ? null : (int) $value;
 	}