Package weight, payload capacity and per-kg payout (ISS-045)

Packages carry a real weightKg (unit weight x count with +/-30% jitter),
plane capacity becomes maxPayloadKg instead of 6 slots, load validation
sums cargo weight against the payload, and the payout gains a per-kg part.
Loadout display shows tonnage; OpenAPI swaps CatalogEntry.capacity for
maxPayloadKg and adds PackageState.weightKg.

lib/game/catalog.ts

@@ -16,8 +16,10 @@ export interface PlaneType {
   // Market price in € (v0.8.0): buying costs `price`, selling pays out
   // SELL_FRACTION × price.
   price: number;
-  // Cargo slot capacity (v0.12.0): how many packages can be loaded on one plane.
-  capacity: number;
+  // Max payload in kg (v0.27.0, ISS-045 — replaces the v0.12.0 slot count): total
+  // package weight that can be loaded on one plane. ATR 72-600-class figure, tuned
+  // so every cargo type at max count × 1.3 jitter still fits alone (see UNIT_WEIGHT_KG).
+  maxPayloadKg: number;
 }
 
 export const PLANE_TYPES: Record<string, PlaneType> = {
@@ -31,7 +33,9 @@ export const PLANE_TYPES: Record<string, PlaneType> = {
     // €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.
     price: 200_000,
-    capacity: 6,
+    // ponytail: balance-tunable payload (kg) — every cargo type at max count × 1.3 jitter
+    // must stay below this so any single package fits alone; typical loads carry ~3–6 packages.
+    maxPayloadKg: 4_800,
   },
 };
 
@@ -57,7 +61,8 @@ export interface CatalogEntry {
   // lib/sim/movement.ts with these + FUEL_DENSITY_KG_PER_L.
   emptyWeightKg: number;
   speedKmh: number;
-  capacity: number;
+  // Max payload in kg (v0.27.0) — total package weight that can be loaded on one plane.
+  maxPayloadKg: number;
 }
 
 // The catalog as a flat array, one entry per plane type — the single source of
@@ -71,6 +76,6 @@ export function catalogEntries(): CatalogEntry[] {
     burnPerKm: t.burnPerKm,
     emptyWeightKg: t.emptyWeightKg,
     speedKmh: t.speedKmh,
-    capacity: t.capacity,
+    maxPayloadKg: t.maxPayloadKg,
   }));
 }