feat(economy): generic atomic profile-economy authority

Add a game-agnostic economy service that exposes atomic, fail-closed
operations over Core's existing durable tables rather than forking a
parallel persistence stack:

  * currency ledger -> clubs.coins
  * owned inventory -> owned_cards
  * entitlements    -> packs (opaque definition_id, consume-once `opened`)

Compound operations run inside a single SQLite transaction, closing the
atomicity gap in the pool-scoped club::{spend,add}_coins helpers whose
read/modify/write spans multiple round-trips. Public ops:

  balance, purchase_entitlement (debit+grant), redeem_entitlement
  (consume-once + add items, all-or-nothing), sell_item (remove+credit),
  grant_reward (credit).

Deliberately game-neutral: currency names, entitlement/pack ids, and
per-save item-id sequences stay in the per-game adapter that drives these
primitives. 9 unit tests cover debit/credit fail-closed rollback,
consume-once, partial-redeem rollback, and non-negative guards.

src/services/mod.rs

@@ -3,6 +3,7 @@ pub mod card_db;
 pub mod checkin;
 pub mod club;
 pub mod draft;
+pub mod economy;
 pub mod event;
 pub mod fut_champs;
 pub mod game_ext;