Fix the Tugboat demo seed for the current slot-category booking API

The Tugboat preview build fails while seeding the demo, in .tugboat/setup.php. The seed pre-dates the split of the booking category into a resource-level BookingCategory plus a slot-level BookingSlotCategory, and it calls the old hold() signature.

It builds a BookingCategory with slot and capacity (those now live on BookingSlotCategory), and calls hold($category, $quantity, $ttl, $reference) where the method is now hold(BookingSlotInterface $slot, ?BookingSlotCategoryInterface $category, int $quantity, ?int $ttl). The build dies with a TypeError, so no preview (including the base branch) can build.

Fix

Update the seed to the current model: create a resource-level category, bind it to each slot through a BookingSlotCategory that carries the per-slot capacity, and hold against the slot with hold($slot, $slotCategory, $quantity). Also correct the stale JSON:API links in the guide page (the booking entity type is yoyaku) and add the slot-category resource.