Currency, storefronts, purchasing (#12)

And a few other minor things, but primarily, the balance table exists and also consumable/inventory table.

apps/econ/migrations/0003_received_gift.sql

@@ -0,0 +1,15 @@
+-- Received gift boxes, owned by the `econ` worker. One row per box: a box is created
+-- when a player buys a storefront item (`/api/storefronts/v2/buyItem`) and deleted when
+-- the client opens it (`/api/avatar/v2/gifts/consume`, on the `api` worker). Opening is
+-- cosmetic — the item is granted into the `inventory` table at purchase time, so a box
+-- carries only its rendered content (`data`) for the gift list. Kept in sync with
+-- RECEIVED_GIFT_SCHEMA_DDL in @repo/domain's gifts-db.ts.
+
+CREATE TABLE IF NOT EXISTS received_gift (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  account_id INTEGER NOT NULL,
+  data TEXT NOT NULL,
+  created_at TEXT NOT NULL
+  );
+
+CREATE INDEX IF NOT EXISTS idx_received_gift_account ON received_gift (account_id);