feat: NPC mourning behavior on housemate death

When an NPC dies from starvation, their highest-familiarity companion enters mourning for 100 ticks (~half a day). Mourning NPCs skip work: they rest if energy is low, otherwise wander near home. Mourning_ticks counts down each tick through ActionExecutionSystem and is serialized for save/load continuity with backward-compatible default of 0. This gives the familiarity graph its first behavioral consequence.

simulation/SimulationManager.gd

@@ -149,6 +149,7 @@ func simulate_tick() -> void:
 			npc_died.emit(npc)
 			npc_task_changed.emit(npc, old_task, npc.current_task)
 			record_narrative_event(SimulationIds.EVENT_NPC_DIED, npc.id)
+			_notify_mourning(npc)
 
 			if debug_logs:
 				print("[SimulationManager] NPC died: ", npc.npc_name)
@@ -491,6 +492,30 @@ func _npc_inventory_id(npc_id: int) -> StringName:
 	return StringName("npc_%d_inventory" % npc_id)
 
 
+func _notify_mourning(dead_npc: SimNPC) -> void:
+	var best_id := -1
+	var best_score := -1.0
+	for key in dead_npc.familiarity:
+		var other_id: int = int(key)
+		var score: float = float(dead_npc.familiarity[key])
+		if score > best_score:
+			best_score = score
+			best_id = other_id
+	if best_id < 0:
+		return
+	for npc in npcs:
+		if npc.id == best_id and not npc.is_dead:
+			npc.mourning_ticks = 100
+			if debug_logs:
+				print(
+					"[SimulationManager] ",
+					npc.npc_name,
+					" is mourning ",
+					dead_npc.npc_name
+				)
+			return
+
+
 func _record_economic_event(
 	event_type: StringName,
 	actor_id: int,