Eingraben: 2 s move inside a barrier turning solid, 4 s duration

The barrier's model alpha goes to opaque over 1 s, the dwarf is moved,
and it clears over 1 s; orders to him are refused meanwhile (new
game::FilterCreatureOrders). The art's duration in its definition is a
fixed 4 s (was 7 + level), which the barrier, its bonus and the tooltip use.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/game/engine/orders.h

@@ -63,6 +63,11 @@ inline void* ControlledCreature(uint8_t* engine) {
 using CreatureOrderFn = void (*)(void* creature, const CreatureOrder& order, void* caller);
 void OnCreatureOrder(CreatureOrderFn callback);
 
+// Asked before the callbacks: an order any filter refuses (returns false) is
+// dropped, the creature never gets it.
+using CreatureOrderFilter = bool (*)(void* creature, const CreatureOrder& order);
+void FilterCreatureOrders(CreatureOrderFilter filter);
+
 // Creature fields.
 constexpr size_t kCreatureId = 0xc;
 constexpr size_t kCreatureX = 0x1c;