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/gin-gonic/gin/internal/bytesconv/bytesconv_1.19.go

@@ -0,0 +1,26 @@
+// Copyright 2020 Gin Core Team. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.20
+
+package bytesconv
+
+import (
+	"unsafe"
+)
+
+// StringToBytes converts string to byte slice without a memory allocation.
+func StringToBytes(s string) []byte {
+	return *(*[]byte)(unsafe.Pointer(
+		&struct {
+			string
+			Cap int
+		}{s, len(s)},
+	))
+}
+
+// BytesToString converts byte slice to string without a memory allocation.
+func BytesToString(b []byte) string {
+	return *(*string)(unsafe.Pointer(&b))
+}

services/payment/vendor/github.com/gin-gonic/gin/internal/bytesconv/bytesconv_1.20.go

@@ -0,0 +1,23 @@
+// Copyright 2023 Gin Core Team. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+//go:build go1.20
+
+package bytesconv
+
+import (
+	"unsafe"
+)
+
+// StringToBytes converts string to byte slice without a memory allocation.
+// For more details, see https://github.com/golang/go/issues/53003#issuecomment-1140276077.
+func StringToBytes(s string) []byte {
+	return unsafe.Slice(unsafe.StringData(s), len(s))
+}
+
+// BytesToString converts byte slice to string without a memory allocation.
+// For more details, see https://github.com/golang/go/issues/53003#issuecomment-1140276077.
+func BytesToString(b []byte) string {
+	return unsafe.String(unsafe.SliceData(b), len(b))
+}

services/payment/vendor/github.com/gin-gonic/gin/internal/json/go_json.go

@@ -0,0 +1,22 @@
+// Copyright 2017 Bo-Yi Wu. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+//go:build go_json
+
+package json
+
+import json "github.com/goccy/go-json"
+
+var (
+	// Marshal is exported by gin/json package.
+	Marshal = json.Marshal
+	// Unmarshal is exported by gin/json package.
+	Unmarshal = json.Unmarshal
+	// MarshalIndent is exported by gin/json package.
+	MarshalIndent = json.MarshalIndent
+	// NewDecoder is exported by gin/json package.
+	NewDecoder = json.NewDecoder
+	// NewEncoder is exported by gin/json package.
+	NewEncoder = json.NewEncoder
+)

services/payment/vendor/github.com/gin-gonic/gin/internal/json/json.go

@@ -0,0 +1,22 @@
+// Copyright 2017 Bo-Yi Wu. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+//go:build !jsoniter && !go_json && !(sonic && avx && (linux || windows || darwin) && amd64)
+
+package json
+
+import "encoding/json"
+
+var (
+	// Marshal is exported by gin/json package.
+	Marshal = json.Marshal
+	// Unmarshal is exported by gin/json package.
+	Unmarshal = json.Unmarshal
+	// MarshalIndent is exported by gin/json package.
+	MarshalIndent = json.MarshalIndent
+	// NewDecoder is exported by gin/json package.
+	NewDecoder = json.NewDecoder
+	// NewEncoder is exported by gin/json package.
+	NewEncoder = json.NewEncoder
+)

services/payment/vendor/github.com/gin-gonic/gin/internal/json/jsoniter.go

@@ -0,0 +1,23 @@
+// Copyright 2017 Bo-Yi Wu. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+//go:build jsoniter
+
+package json
+
+import jsoniter "github.com/json-iterator/go"
+
+var (
+	json = jsoniter.ConfigCompatibleWithStandardLibrary
+	// Marshal is exported by gin/json package.
+	Marshal = json.Marshal
+	// Unmarshal is exported by gin/json package.
+	Unmarshal = json.Unmarshal
+	// MarshalIndent is exported by gin/json package.
+	MarshalIndent = json.MarshalIndent
+	// NewDecoder is exported by gin/json package.
+	NewDecoder = json.NewDecoder
+	// NewEncoder is exported by gin/json package.
+	NewEncoder = json.NewEncoder
+)

services/payment/vendor/github.com/gin-gonic/gin/internal/json/sonic.go

@@ -0,0 +1,23 @@
+// Copyright 2022 Gin Core Team. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+//go:build sonic && avx && (linux || windows || darwin) && amd64
+
+package json
+
+import "github.com/bytedance/sonic"
+
+var (
+	json = sonic.ConfigStd
+	// Marshal is exported by gin/json package.
+	Marshal = json.Marshal
+	// Unmarshal is exported by gin/json package.
+	Unmarshal = json.Unmarshal
+	// MarshalIndent is exported by gin/json package.
+	MarshalIndent = json.MarshalIndent
+	// NewDecoder is exported by gin/json package.
+	NewDecoder = json.NewDecoder
+	// NewEncoder is exported by gin/json package.
+	NewEncoder = json.NewEncoder
+)