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/resource_nodes/ResourceNode.tscn

@@ -0,0 +1,25 @@
+[gd_scene load_steps=3 format=3 uid="uid://r3s0urc3tscn01"]
+
+[ext_resource type="Script" uid="uid://r3s0urc3n0d3v1" path="res://world/resource_nodes/ResourceNode.gd" id="1_abcde"]
+
+[sub_resource type="BoxMesh" id="BoxMesh_visual"]
+
+[node name="ResourceNode" type="Node3D"]
+script = ExtResource("1_abcde")
+
+[node name="Visual" type="Node3D" parent="."]
+
+[node name="MeshInstance3D" type="MeshInstance3D" parent="Visual"]
+mesh = SubResource("BoxMesh_visual")
+
+[node name="InteractionPoint" type="Marker3D" parent="."]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 2.0)
+
+[node name="DebugLabel" type="Label3D" parent="."]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 2.0, 0)
+billboard = 1
+no_depth_test = true
+font_size = 24
+outline_modulate = Color(0, 0, 0, 1)
+outline_size = 4
+text = "INIT"