Add monetization app with RevenueCat webhooks alongside Stripe.

Rename finance → monetization (keep finance_* tables via app label), add
RevenueCat webhook + ledger upserts so store IAP syncs subscriptions and
billing history like Stripe. Companion to chat_web_app#100 / #68.

.env.example

@@ -76,13 +76,17 @@ OAUTH_CALLBACK_BASE_URL=http://127.0.0.1:8001
 #   POST {OAUTH_CALLBACK_BASE_URL}/api/drive/webhooks/microsoft/
 # Worker sync: `python manage.py sync_drive_connections [--connection-id N]`
 
-# Stripe / finance (optional local — required for checkout + webhooks)
+# Stripe / monetization (optional local — required for checkout + webhooks)
 STRIPE_SECRET_KEY=
 STRIPE_PUBLISHABLE_KEY=
 STRIPE_WEBHOOK_SECRET=
 # Optional: pre-created Stripe Price ID for Founders. When empty, Checkout uses
 # SubscriptionPlan.price_cents / SUBSCRIPTION_PRICE_* ($10 USD / month Founders).
 STRIPE_PRICE_ID=
+# RevenueCat webhook Authorization bearer secret (store IAP).
+REVENUECAT_WEBHOOK_SECRET=
+# Optional JSON map of store product id → plan slug, e.g.
+# REVENUECAT_PRODUCT_PLAN_MAP={"hesychia_founders_monthly":"founders"}
 # SUBSCRIPTION_PRICE_AMOUNT_CENTS=1000
 # SUBSCRIPTION_PRICE_CURRENCY=usd
 # SUBSCRIPTION_PRICE_INTERVAL=month