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>

plans/chains/nike_deimos_lst.yaml

@@ -0,0 +1,8 @@
+# Multi-base chain: Nike mines LST, ships it to Deimos, Deimos turns it (+ market AL) into BSE.
+# trip_cost/cargo are placeholders (see tools/network.py) until a real fuel model exists.
+name: "Nike LST -> Deimos PP2 (BSE)"
+bases:
+  nike: {plan: plans/examples/nike_lst_ext.yaml, cm_free: true}   # founded via the faction expansion contract's kit
+  deimos: plans/examples/deimos_pp2_bse.yaml
+transfers:
+  - {material: LST, src: nike, dst: deimos, trip_cost: 9250, cargo: 500}