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/state.ts

@@ -50,6 +50,8 @@ export interface PackageState {
   reward: number;
   cargoType: string;
   cargoCount: number;
+  // Package weight in kg (v0.27.0, ISS-045) — drives load validation + per-kg payout.
+  weightKg: number;
   deadlineSimTime: number;
   status: 'open' | 'loaded' | 'delivered' | 'expired' | 'abandoned';
   planeId: string | null;
@@ -135,6 +137,7 @@ export async function getStateSnapshot(): Promise<StateSnapshot> {
       reward: p.reward,
       cargoType: p.cargoType,
       cargoCount: p.cargoCount,
+      weightKg: p.weightKg,
       deadlineSimTime: p.deadlineSimTime,
       status: p.status,
       planeId: p.planeId,