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.

app/api/state/route.test.ts

@@ -58,7 +58,7 @@ describe('GET /api/state', () => {
 
     const packages = body.packages as Array<Record<string, unknown>>;
     expect(packages.length).toBeGreaterThan(0);
-    for (const key of ['id', 'originIcao', 'destIcao', 'reward', 'cargoType', 'deadlineSimTime', 'status']) {
+    for (const key of ['id', 'originIcao', 'destIcao', 'reward', 'cargoType', 'weightKg', 'deadlineSimTime', 'status']) {
       expect(packages[0], `package.${key}`).toHaveProperty(key);
     }
   });
@@ -86,7 +86,7 @@ describe('GET /api/state', () => {
       expect(entry.maxFuel).toBe(type.maxFuel);
       expect(entry.burnPerKm).toBe(type.burnPerKm);
       expect(entry.speedKmh).toBe(type.speedKmh);
-      expect(entry.capacity).toBe(type.capacity); // v0.12.0 slot capacity (ATR 72-600: 6)
+      expect(entry.maxPayloadKg).toBe(type.maxPayloadKg); // v0.27.0 payload kg (ATR 72-600: 4800)
     }
 
     // Economy constants — the single source of truth stays lib/game/catalog.ts.