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/db/schema.ts

@@ -37,6 +37,9 @@ export const packages = sqliteTable('packages', {
   reward: real('reward').notNull(),
   cargoType: text('cargo_type').notNull(),
   cargoCount: integer('cargo_count').notNull(),
+  // Package weight in kg (v0.27.0, ISS-045) — drives load validation (plane payload)
+  // and the per-kg part of the payout. Pre-existing rows backfill to the default.
+  weightKg: real('weight_kg').notNull().default(2000),
   deadlineSimTime: integer('deadline_sim_time').notNull(),
   // 'expired' = an open OR loaded package whose deadline passed on a tick. Loaded
   // expired packages keep occupying their slot, deliver no reward, and abandon free.