Add multi-base chain modelling, fix price-band-aware demand/supply, tranche-split sell tool

- puga/network.py + tools/network.py: model a multi-base chain (e.g. mine LST at one base,
  ship it, consume it at another). Simulates each base independently, nets a transferred
  material's producer-surplus against consumer-need, charges real freight only on what's
  moved, cm_free for a founding covered by a Core Module Kit. Worked example in plans/chains/.
- puga/saturation.py: real price-band filtering. FIO's order_book NarrowPriceBandLow/High and
  WidePriceBandLow/High match APEX's own displayed Price Band exactly (verified live) - an
  order outside it is a stale artifact, not just uncompetitive. Added in_band() and
  effective_demand(); effective_supply() gained the same hard band filter alongside its
  existing soft vwap-proximity filter (renamed that param mult to free up `band`). Wired into
  tools/scan.py stage 2 in place of the raw, unfiltered demand figure. Was flagged as an
  unimplemented refinement in saturation-design.md since the original design review.
- tools/sell.py: self-contained tranche split (aggressive tranche capped at a volume quantile,
  median normally or 80th pct with --tight when a payment is imminent and stockout risk
  outweighs margin; patient tranche priced under the next competitor tier). Instant-bid
  comparison moved behind --show-bid (off by default).
- Docs and roadmap updated accordingly.

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

puga/network.py

@@ -0,0 +1,60 @@
+"""Multi-base chains: combine several independently-simulated plans into one balance sheet.
+
+Each base is simulated on its own (puga.simulate.simulate), which prices every flow at market —
+that already gives each base's own correct profit whether or not a material actually leaves the
+base. For a material transferred between two bases in the SAME chain (e.g. LST mined at Nike,
+consumed at Deimos), the two bases' market-priced flows cancel out in the combined total to within
+the transferred quantity (base A "sells" it, base B "buys" it, at the same price basis) — so the
+combined total needs only ONE correction: the real freight cost of physically moving it, which
+isn't in either base's isolated numbers. Leftover surplus (more produced than a partner needs) is
+still validly sold at market by the producing base; leftover deficit is still validly bought.
+"""
+from dataclasses import dataclass, field
+from . import fio
+from .simulate import simulate
+
+
+@dataclass
+class BaseNode:
+    name: str
+    plan: dict
+    recipes: list
+    buildings: list
+    resources: list
+    fertility: float
+    price: callable
+    faction: str | None = None
+    permits: tuple[float, float] = (1, 2)
+    built: dict = field(default_factory=dict)
+
+
+@dataclass
+class Transfer:
+    material: str
+    src: str                    # producing base's name (key in the `bases` dict)
+    dst: str                    # consuming base's name
+    trip_cost: float = 9250.0   # AIC per round trip; PLACEHOLDER until a real route/fuel model exists
+    cargo: float = 500.0        # t or m3 per trip
+
+
+def combine(bases: dict[str, BaseNode], transfers: list[Transfer]) -> dict:
+    mat = {m["Ticker"]: m for m in fio.materials()}
+    results = {name: simulate(b.plan, b.recipes, b.buildings, b.resources, b.fertility, b.price, b.faction, b.permits, built=b.built)
+               for name, b in bases.items()}
+    ledger = []
+    total_profit = sum(r["profit"] for r in results.values())
+    for t in transfers:
+        prod = results[t.src]["flows"].get(t.material, {"out": 0.0, "inp": 0.0})
+        cons = results[t.dst]["flows"].get(t.material, {"out": 0.0, "inp": 0.0})
+        avail = prod["out"] - prod["inp"]          # net surplus at the source (0 if it's a net consumer)
+        need = cons["inp"] - cons["out"]            # net requirement at the destination
+        moved = max(0.0, min(avail, need))
+        m = mat.get(t.material)
+        weight, volume = moved * (m["Weight"] if m else 0), moved * (m["Volume"] if m else 0)
+        trips = max(weight, volume) / t.cargo if t.cargo else 0.0
+        freight = trips * t.trip_cost
+        total_profit -= freight
+        ledger.append(dict(material=t.material, src=t.src, dst=t.dst, moved=moved, avail=avail, need=need,
+                            shortfall=max(0.0, need - avail), surplus=max(0.0, avail - need),
+                            weight=weight, volume=volume, trips=trips, freight=freight))
+    return dict(results=results, ledger=ledger, total_profit=total_profit)