feat: v0.16.0 — ISS-005 weight-proportional fuel burn + refuel just enough for the loaded package

Part A: r(F) = k(We + rho*F) L/km, k calibrated so a full tank burns exactly
the old constant; closed forms in lib/sim/movement.ts (fuelAtWeighted,
requiredFuelFor, burnRateConstant, FUEL_DENSITY_KG_PER_L). Catalog gains
emptyWeightKg (ATR72 OEW 9300 kg), exposed in the snapshot. All three burn
call sites (engine landing, state live fuel, fly validation) moved to the
weighted model; old constant-rate fuelAt removed.

Part B: POST /api/planes/{planeId}/refuel takes an optional body
{mode:'full'|'forFlight', packageId} — no body keeps today's fill-to-full
behavior exactly (fuel lands bit-exact on maxFuel); forFlight adds just
enough for the loaded package's destination leg (409 not-loaded/expired/
doesn't-fit, 400 bad body). UI: per-cargo-row 'Refuel' button
(refuel-for-{pkg.id}), market button renamed 'Refuel to full'.

OpenAPI: RefuelRequest schema + optional requestBody + 400 on refuel, fly's
409 description updated, CatalogEntry.emptyWeightKg. Tests: new weighted-burn
suite, forFlight action/route cases (incl. ~7670 km UNNT<->LPPD doesn't-fit),
openapi guards; landing-fuel assertions in engine.test.ts + e2e/actions.spec.ts
use the closed form; the e2e 'return leg unfuelable' scenario reworked — a full
tank now covers the EDDF<->LEZL round trip, so the 409 moves to the second
outbound. New e2e: row Refuel deducts exactly L*price / raises fuel by exactly
L via the endpoint's own response snapshot.

lib/game/catalog.ts

@@ -6,8 +6,11 @@ export interface PlaneType {
   name: string;
   // Fuel capacity, liters.
   maxFuel: number;
-  // Fuel burn per km of flight, liters/km (cruise).
+  // Fuel burn per km of flight at a FULL tank, liters/km (cruise) — the weighted burn
+  // model (v0.16.0) calibrates its rate constant to this value at F = maxFuel.
   burnPerKm: number;
+  // Operating empty weight in kg (v0.16.0) — feeds the weight-proportional burn model.
+  emptyWeightKg: number;
   // Cruise speed, km/h — used by the sim tick to advance planes along routes.
   speedKmh: number;
   // Market price in € (v0.8.0): buying costs `price`, selling pays out
@@ -22,7 +25,8 @@ export const PLANE_TYPES: Record<string, PlaneType> = {
     id: 'atr72',
     name: 'ATR 72-600',
     maxFuel: 6300,
-    burnPerKm: 1.75, // ~900 kg/h at 510 km/h cruise (Jet-A1 ≈ 0.8 kg/L)
+    burnPerKm: 1.75, // full-tank rate: ~893 L/h ≈ 714 kg/h at 510 km/h cruise (Jet-A1 ≈ 0.8 kg/L); the weighted model burns less as fuel drops off
+    emptyWeightKg: 9_300, // ATR 72-600 operating empty weight
     speedKmh: 510,
     // €200k — with the starting cash of €20k and typical hop rewards (~€1–3k),
     // a second ATR takes sustained play to afford, as intended for the MVP sink.
@@ -49,6 +53,9 @@ export interface CatalogEntry {
   price: number;
   maxFuel: number;
   burnPerKm: number;
+  // Weighted burn model inputs (v0.16.0) — clients can mirror the closed forms in
+  // lib/sim/movement.ts with these + FUEL_DENSITY_KG_PER_L.
+  emptyWeightKg: number;
   speedKmh: number;
   capacity: number;
 }
@@ -62,6 +69,7 @@ export function catalogEntries(): CatalogEntry[] {
     price: t.price,
     maxFuel: t.maxFuel,
     burnPerKm: t.burnPerKm,
+    emptyWeightKg: t.emptyWeightKg,
     speedKmh: t.speedKmh,
     capacity: t.capacity,
   }));