feat(payment): standalone ZarinPal broker on pay.flatrender.ir

A generic multi-client payment gateway so FlatRender, meezi.ir and
bargevasat.ir can all pay through ZarinPal's single verified callback
domain (pay.flatrender.ir).

New Go service services/payment (clones the notification skeleton +
vendored deps):
- migration 31_payment_broker.sql — `payment` schema: client_apps,
  transactions, webhook_deliveries.
- ZarinPal v4 client ported from the proven identity PaymentService
  (request.json -> StartPay -> verify.json; codes 100/101).
- client API: POST /v1/pay/request + /v1/pay/inquiry, authed by
  X-Api-Key + HMAC body signature; GET /callback/zarinpal (the single
  verified endpoint) verifies, then 302s the user back to the site's
  return_url (signed) and fires a signed, retried webhook.
- per-client ZarinPal merchant override (default = shared merchant);
  amount stored canonically in Rial, unit to ZarinPal env-configurable.
- admin API /v1/admin/* (FlatRender admin JWT): client-app CRUD +
  key issue/rotate + transactions list.

Deploy wiring: payment-svc in docker-compose.v2.yml (host port 1607),
pay.flatrender.ir server block in mirror-nginx conf, ENV_FILE +
README updates (cert SAN + manual migration note).

Admin UI: src/components/admin/PaymentsAdmin.tsx (client apps with
one-time key reveal + rotate, transactions table) + /admin/payments
page + nav link + fa/en strings; pay-admin proxy route to payment-svc.

Docs/SDK: deploy/PAYMENTS.md (integration contract) + deploy/sdk/flatpay.js
(zero-dep Node client + webhook verifier) for meezi/any site.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/payment/vendor/github.com/modern-go/reflect2/README.md

@@ -0,0 +1,71 @@
+# reflect2
+
+[![Sourcegraph](https://sourcegraph.com/github.com/modern-go/reflect2/-/badge.svg)](https://sourcegraph.com/github.com/modern-go/reflect2?badge)
+[![GoDoc](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)](http://godoc.org/github.com/modern-go/reflect2)
+[![Build Status](https://travis-ci.org/modern-go/reflect2.svg?branch=master)](https://travis-ci.org/modern-go/reflect2)
+[![codecov](https://codecov.io/gh/modern-go/reflect2/branch/master/graph/badge.svg)](https://codecov.io/gh/modern-go/reflect2)
+[![rcard](https://goreportcard.com/badge/github.com/modern-go/reflect2)](https://goreportcard.com/report/github.com/modern-go/reflect2)
+[![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://raw.githubusercontent.com/modern-go/reflect2/master/LICENSE)
+
+reflect api that avoids runtime reflect.Value cost
+
+* reflect get/set interface{}, with type checking
+* reflect get/set unsafe.Pointer, without type checking
+* `reflect2.TypeByName` works like `Class.forName` found in java
+
+[json-iterator](https://github.com/json-iterator/go) use this package to save runtime dispatching cost.
+This package is designed for low level libraries to optimize reflection performance.
+General application should still use reflect standard library.
+
+# reflect2.TypeByName
+
+```go
+// given package is github.com/your/awesome-package
+type MyStruct struct {
+	// ...
+}
+
+// will return the type
+reflect2.TypeByName("awesome-package.MyStruct")
+// however, if the type has not been used
+// it will be eliminated by compiler, so we can not get it in runtime
+```
+
+# reflect2 get/set interface{}
+
+```go
+valType := reflect2.TypeOf(1)
+i := 1
+j := 10
+valType.Set(&i, &j)
+// i will be 10
+```
+
+to get set `type`, always use its pointer `*type`
+
+# reflect2 get/set unsafe.Pointer
+
+```go
+valType := reflect2.TypeOf(1)
+i := 1
+j := 10
+valType.UnsafeSet(unsafe.Pointer(&i), unsafe.Pointer(&j))
+// i will be 10
+```
+
+to get set `type`, always use its pointer `*type`
+
+# benchmark
+
+Benchmark is not necessary for this package. It does nothing actually.
+As it is just a thin wrapper to make go runtime public. 
+Both `reflect2` and `reflect` call same function 
+provided by `runtime` package exposed by go language.
+
+# unsafe safety
+
+Instead of casting `[]byte` to `sliceHeader` in your application using unsafe.
+We can use reflect2 instead. This way, if `sliceHeader` changes in the future,
+only reflect2 need to be upgraded.
+
+reflect2 tries its best to keep the implementation same as reflect (by testing).