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
