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.

e2e/right-pane.spec.ts

@@ -42,7 +42,7 @@ interface CatalogEntry {
   burnPerKm: number;
   emptyWeightKg: number; // v0.16.0 weighted burn input
   speedKmh: number;
-  capacity: number;
+  maxPayloadKg: number; // v0.27.0 — replaces the v0.12.0 slot capacity
 }
 
 interface StateBody {
@@ -309,7 +309,7 @@ test('market buy/sell render with previews from the catalog in /api/state; left-
   const body = await getState(page); // authoritative catalog + economy constants (v0.10.0)
   expect(body.catalog.length).toBeGreaterThan(0);
   const entry = body.catalog.find((e) => e.model === 'atr72')!;
-  expect(entry.capacity).toBe(6); // v0.12.0 slot capacity exposed in the snapshot
+  expect(entry.maxPayloadKg).toBe(4_800); // ATR 72-600 max payload (lib/game/catalog.ts)
 
   await page.goto('/');
   // Buy: the model picker lists the catalog entry and the price preview is its full price.