feat: add ResourceNode system with target selection and reservation

Phase 1-2 of the ResourceNode migration plan:

- Create ResourceNode class (world/resource_nodes/) with extraction,
  reservation, nearest-available selection, and debug label
- Place 4 resource instances in main.tscn (2 berry bushes, 2 trees)
- Add target_id to SimNPC for tracking which node an NPC is using
- Add set_npc_target_id and release_npc_reservation to SimulationManager
  with cleanup on task change, completion, and death
- Update WorldViewManager to query available ResourceNodes first,
  falling back to zone markers with a logged warning

world/world_view_manager.gd

@@ -83,6 +83,11 @@ func update_npc_targets() -> void:
 			continue
 
 		var visual = active_npc_visuals[npc.id]
+		var resource_pos := _try_get_resource_target(npc, npc.current_task)
+		if resource_pos != null:
+			visual.set_target_position(resource_pos)
+			continue
+
 		var target := get_target_for_task(npc.current_task)
 
 		if target == null:
@@ -108,6 +113,32 @@ func get_target_for_task(task: String) -> Marker3D:
 		_:
 			return rest_zone
 
+func _try_get_resource_target(npc: SimNPC, task: String):
+	var action_map := {
+		"gather_food": &"gather_food",
+		"gather_wood": &"gather_wood"
+	}
+	var action_id := action_map.get(task) as StringName
+	if action_id == null:
+		return null
+
+	var visual = active_npc_visuals.get(npc.id) as Node3D
+	if visual == null:
+		return null
+
+	var node := ResourceNode.find_available(action_id, npc.id, visual.global_position)
+	if node == null:
+		debug_log("No available resource node for %s, using zone fallback" % task)
+		return null
+
+	if not node.reserve(npc.id):
+		debug_log("Failed to reserve %s for %s" % [node.node_id, npc.npc_name])
+		return null
+
+	npc.target_id = node.node_id
+	debug_log("%s reserved %s for %s" % [npc.npc_name, node.node_id, task])
+	return node.interaction_point.global_position
+
 func _on_npc_task_changed(npc: SimNPC, old_task: String, new_task: String) -> void:
 	if DEBUG_LOGS:
 		debug_log("%s changed task: %s -> %s" % [npc.npc_name, old_task, new_task])
@@ -116,6 +147,11 @@ func _on_npc_task_changed(npc: SimNPC, old_task: String, new_task: String) -> vo
 		return
 	
 	var visual = active_npc_visuals[npc.id]
+	var resource_pos := _try_get_resource_target(npc, new_task)
+	if resource_pos != null:
+		visual.set_target_position(resource_pos)
+		return
+	
 	var target := get_target_for_task(new_task)
 	
 	if target != null: