Add a resource type with per-customer exclusivity (one active booking across the type)

Some resources are mutually exclusive per customer: a customer may hold only one active booking across a whole group of them at once. The motivating case is mountain refuges, where a hiker can book one refuge among all available refuges, not several. The engine has no way to group resources today (the pricing category is a per-slot tier, not a resource grouping), so this cannot be expressed.

Proposed resolution

Introduce a resource type, and express the rule as another order constraint on top of the system added in #3609485. Mutual exclusion is a property of the set, not of each resource, so it belongs on the type.

• A yoyaku_resource_type config entity (id, label, and an exclusive_per_customer flag), with schema, mirroring the existing tenant config entity. It is the home for type-level policy and can carry more later.
• A type entity-reference field on BookingResource, with a getType() accessor.
• A single_active_per_type OrderConstraint plugin: self-gating, it only bites on lines whose resource belongs to a type flagged exclusive_per_customer, then counts the customer's active (held or confirmed) bookings across every resource of that type (by the order's email) and reports a violation once more than one exists. The type is the exclusivity pool.

Enforcement reuses the OrderConstraintManager from #3609485 (confirmOrder plus validateOrder), so no new trigger wiring is needed.

Tests

OrderConstraintTest gains coverage: an exclusive type refuses a second booking across two of its resources, a different email does not collide, and a non-exclusive type allows several.