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/state.ts

@@ -3,7 +3,7 @@ import { haversineKm } from '@/lib/geo';
 import { getGameDb } from '@/lib/db/client';
 import * as schema from '@/lib/db/schema';
 import { catalogEntries, FUEL_PRICE_PER_L, PLANE_TYPES, SELL_FRACTION, type CatalogEntry } from './catalog';
-import { fuelAt, progressAt, positionAt } from '@/lib/sim/movement';
+import { fuelAtWeighted, progressAt, positionAt } from '@/lib/sim/movement';
 
 // Read-only game-state snapshot for client polling (GET /api/state).
 
@@ -84,7 +84,7 @@ export async function getStateSnapshot(): Promise<StateSnapshot> {
     const distanceKm = haversineKm(from.lat, from.lon, to.lat, to.lon);
     const progress = progressAt(p.departureSimTime, distanceKm, type.speedKmh, simRow.clockMs);
     const pos = positionAt(from.lat, from.lon, to.lat, to.lon, progress);
-    return { ...pos, fuel: fuelAt(p.fuel, type.burnPerKm, distanceKm, progress) };
+    return { ...pos, fuel: fuelAtWeighted(p.fuel, type.burnPerKm, type.emptyWeightKg, type.maxFuel, distanceKm, progress) };
   };
 
   return {