docs: choose BTCPay for payments

docs/ops/deployment.md

@@ -16,6 +16,7 @@ Deploy on one VPS with Docker Compose.
 - `postgres`: primary database
 - `caddy`: TLS termination and reverse proxy
 - optional `minio`: self-hosted object storage for single-server deployments
+- `btcpay`: self-hosted payment stack for crypto invoice checkout
 
 ## Deployment notes
 - Run one Compose project on a single server.
@@ -23,6 +24,8 @@ Deploy on one VPS with Docker Compose.
 - Keep secrets in server-side environment files or a secret manager.
 - Back up PostgreSQL and object storage separately.
 - Prefer Telegram long polling to avoid an extra public webhook surface for the bot.
+- Keep BTCPay persistent data and wallet material isolated from app volumes and back them up separately.
+- If BTCPay requires auxiliary services, treat them as part of the payment stack rather than as app-internal services.
 
 ## Upgrade strategy
 - Build new images.
@@ -42,7 +45,9 @@ Deploy on one VPS with Docker Compose.
 - provision DNS and TLS
 - provision PostgreSQL storage
 - provision S3-compatible storage or enable local MinIO
+- provision BTCPay Server storage and wallet backup path
 - create `.env`
 - deploy Compose stack
 - run database migration job
 - verify web health, worker job loop, and bot polling
+- verify BTCPay invoice creation, callback delivery, and payout/reconciliation procedures