Resolve #3609086 "Fix the Tugboat demo seed for the current slot-category booking API"

Frank Mablyrequested to merge
issue/yoyaku-3609086:3609086-tugboat-seed into 1.x

Fixes the demo seed in .tugboat/setup.php to the current booking model: resource-level BookingCategory + slot-level BookingSlotCategory carrying capacity, and hold($slot, $slotCategory, $quantity). Also corrects the guide's JSON:API links (booking entity type is yoyaku) and adds the slot-category resource.

Closes #3609086.

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