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/client.ts

@@ -40,6 +40,7 @@ CREATE TABLE IF NOT EXISTS packages (
   reward REAL NOT NULL,
   cargo_type TEXT NOT NULL,
   cargo_count INTEGER NOT NULL,
+  weight_kg REAL NOT NULL DEFAULT 2000,
   deadline_sim_time INTEGER NOT NULL,
   status TEXT NOT NULL,
   plane_id TEXT,
@@ -77,6 +78,10 @@ function migrateColumns(raw: RawSqlJsDatabase): void {
   if (!cols('planes').has('queue')) {
     raw.exec(`ALTER TABLE planes ADD COLUMN queue TEXT NOT NULL DEFAULT '[]'`);
   }
+  // v0.27.0 (ISS-045): package weight — pre-existing rows backfill to a mid-range default.
+  if (!cols('packages').has('weight_kg')) {
+    raw.exec('ALTER TABLE packages ADD COLUMN weight_kg REAL NOT NULL DEFAULT 2000');
+  }
 }
 
 // v0.12.0 one-time migration: contracts world → packages world. Detected by the