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/actions/ActionExecutionSystem.gd

@@ -6,6 +6,8 @@ func advance_npc(npc: SimNPC, village: SimVillage) -> void:
 	if npc.is_dead:
 		return
 	_update_needs(npc, village)
+	if npc.mourning_ticks > 0:
+		npc.mourning_ticks -= 1
 	if npc.is_dead or npc.task_state != SimNPC.TASK_STATE_WORKING:
 		return
 	npc.task_progress += 1.0

simulation/actions/ActionSelectionSystem.gd

@@ -34,6 +34,14 @@ func select_action(npc: SimNPC, village: SimVillage, time_of_day: float = 0.5, a
 		return ActionSelectionResult.new(
 			SimulationIds.ACTION_GATHER_FOOD, -1.0, "Starving; must find food"
 		)
+	if npc.mourning_ticks > 0:
+		if npc.energy < 40.0:
+			return ActionSelectionResult.new(
+				SimulationIds.ACTION_REST, -1.0, "Mourning; seeking rest"
+			)
+		return ActionSelectionResult.new(
+			SimulationIds.ACTION_WANDER, -1.0, "Mourning; wandering near home"
+		)
 	if npc.hunger > 80.0:
 		if npc.get_inventory_amount(SimulationIds.RESOURCE_FOOD) >= 1.0:
 			return ActionSelectionResult.new(