feat(server): early subscription for iap (#13826)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a mutation to request/apply a subscription by transaction ID
(client mutation and server operation), returning subscription details.
* **Bug Fixes / Improvements**
* More robust external subscription sync with safer conflict detection,
optional short-lived confirmation, improved parsing and error logging.
* **Chores**
  * Standardized time constants for clarity.
* **Tests**
* Updated subscription test data (expiration date) to reflect new
lifecycle expectations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/__tests__/payment/revenuecat.spec.ts

@@ -497,7 +497,7 @@ test('should remove or cancel the record and revoke entitlement when a trialing
         isTrial: false,
         isActive: false,
         latestPurchaseDate: new Date('2025-04-01T00:00:00.000Z'),
-        expirationDate: new Date('2024-01-01T00:00:00.000Z'),
+        expirationDate: new Date('2025-04-08T00:00:00.000Z'),
         productId: 'app.affine.pro.Annual',
         store: 'app_store',
         willRenew: false,