feat: sync rcat data (#13628)

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

* **New Features**
* RevenueCat support: public webhook endpoint, webhook handler/service,
nightly reconciliation and per-user sync; subscriptions now expose
provider and iapStore; new user-facing error for App Store/Play-managed
subscriptions.
* **Chores**
* Multi-provider subscription schema (Provider, IapStore); Stripe
credentials moved into payment.stripe (top-level apiKey/webhookKey
deprecated); new payment.revenuecat config and defaults added.
* **Tests**
  * Comprehensive RevenueCat integration test suite and snapshots.
* **Documentation**
  * Admin config descriptions updated with deprecation guidance.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/admin/src/config.json

@@ -400,18 +400,23 @@
     },
     "apiKey": {
       "type": "String",
-      "desc": "Stripe API key to enable payment service.",
+      "desc": "[Deprecated] Stripe API key. Use payment.stripe.apiKey instead.",
       "env": "STRIPE_API_KEY"
     },
     "webhookKey": {
       "type": "String",
-      "desc": "Stripe webhook key to enable payment service.",
+      "desc": "[Deprecated] Stripe webhook key. Use payment.stripe.webhookKey instead.",
       "env": "STRIPE_WEBHOOK_KEY"
     },
     "stripe": {
       "type": "Object",
-      "desc": "Stripe sdk options",
+      "desc": "Stripe sdk options and credentials",
       "link": "https://docs.stripe.com/api"
+    },
+    "revenuecat": {
+      "type": "Object",
+      "desc": "RevenueCat integration configs",
+      "link": "https://www.revenuecat.com/docs/"
     }
   },
   "worker": {