Cryptid Core Co Field Operations

v0.8.0-d — Stage 8d: Locate & Biomes

Added
- /locate structure support for all six buildings (Boat House, Weir,
  Campsite, Field Station, Abandoned Field Station, Watchtower) via full
  conversion to the structure system; generation output identical to the
  old feature placement, rarities preserved via random_spread spacing,
  minimum separation now guaranteed
- Cartographer trades: Field Station Map (level 4) and Abandoned Station
  Map (level 5), 13 emeralds + empty map, vanilla treasure-map behavior
- Four registered biomes: Piney Creek Hollow (promoted from the Stage 2
  birch injection), Piney Woods, Misty Pine Ridge, Sunken Grove — complete
  with effects, quiet-woods no-hostile spawn tables, deer variant
  dispatch, berry patches, and building eligibility (natural overworld
  placement still pending the TerraBlender/biome injection fix — see
  STAGE8D_NOTES)

Changed
- Old worlds keep all existing buildings; new chunks generate buildings
  through the structure system (Option A migration — no world regen)