docs: integration guides for mobile customer, POS, EnakGame and backoffice

One guide per team, covering EnakPoint, EnakCoin, EnakGame and vouchers:

- integration-mobile-customer.md: wallet, history (with the game and voucher
  ledger types), push, PIN, exchange, transfer, game list and webview, play
  history, voucher catalog, redeem and my vouchers.
- integration-pos.md: linking customers to orders, earning, receipts,
  void/refund, and vouchers as a known gap (no POS endpoint to mark one used).
- integration-enakgame.md: the Phaser client's side of a play: start with
  Idempotency-Key, complete, rewards, spin, expiry and refunds, retries.
- integration-backoffice.md: loyalty settings and customer wallets, plus
  games, reward configs, spin setup, budgets, metrics and recommendations,
  events, vouchers and code import, analytics.

The JS bridge between the app and the game is a proposal both teams still
have to agree on. Replaces api-enakpoint.md, integration-enakpoint.md,
mobile-customer-enakpoint.md, backoffice-enakpoint.md and enakgame-spin.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/prd-point-coin.md

@@ -388,7 +388,8 @@ beredar. Karena itu:
 > **Diganti EnakGame (2026-10-07).** Alur game di bawah (`POST /customer/spin`,
 > `metadata.coin_cost`, `game_plays`) sudah dihapus. Game sekarang dimainkan lewat
 > `/customer/enakgame/sessions` dengan `games.entry_cost`; lihat
-> [RFC EnakGame](rfc-enakgame.md) §14 dan [enakgame-spin.md](enakgame-spin.md).
+> [RFC EnakGame](rfc-enakgame.md) §14, [integration-backoffice.md](integration-backoffice.md) §8.4,
+> dan [integration-enakgame.md](integration-enakgame.md).
 > EnakCoin tetap mata uang untuk bermain game.
 
 - **Semua jenis game** (`SPIN`, ferris wheel, `RAFFLE`, `MINIGAME`) memotong EnakCoin