Add planet environment-extra materials to capex calcs; buildcost.py tool

Every building needs a planet-hazard material bundle on top of its normal
BuildingCosts (SEA for low pressure, HSE for high pressure, MGC for low
gravity, BL for high gravity, INS for cold, TSH for heat - area-scaled
where applicable), confirmed against live in-game build panels on Nike.
FIO's own BuildRequirements field is an unreliable superset across hazard
types, not a direct per-building list - don't use it directly.

- puga/planet.py::environment_extras(): the real threshold table.
- tools/buildcost.py: full construction material list for one building,
  optionally on a given planet.
- Wired into whatif.py/buy.py (via simulate(planet=...)) and scan.py's
  own bcost(), so their capex numbers stop silently omitting this.
- docs/mechanics.md: the rule, plus a separate forum-sourced note on the
  CX order-cancellation penalty.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tools/scan.py

@@ -13,6 +13,7 @@ from pathlib import Path
 import yaml
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
 from puga import ROOT, config, econ, fio, market, prunplanner as pp, saturation as sat
+from puga import planet as pl
 
 TIER_CODE = {"pioneer": "P", "settler": "S", "technician": "T", "engineer": "E", "scientist": "Sc"}
 TIER_RANK = {"P": 0, "S": 1, "T": 2, "E": 3, "Sc": 4}
@@ -83,7 +84,14 @@ def main():
         parts = [(x["Amount"], ask(x["CommodityTicker"])) for x in b["BuildingCosts"]]
         if any(p is None for _, p in parts):
             return None
-        return sum(n * p for n, p in parts) + a.mcg * b["AreaCost"] * mcg
+        cost = sum(n * p for n, p in parts) + a.mcg * b["AreaCost"] * mcg
+        if planet is not None:
+            extras = pl.environment_extras(planet, b["AreaCost"])
+            prices = {etk: ask(etk) for etk in extras}
+            if any(p is None for p in prices.values()):
+                return None
+            cost += sum(qty * prices[etk] for etk, qty in extras.items())
+        return cost
 
     hab_head, hab_area = {}, {}
     for tier, hab in (("pioneer", "HB1"), ("settler", "HB2"), ("technician", "HB3"), ("engineer", "HB4"), ("scientist", "HB5")):