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/goccy/go-json/query.go

@@ -0,0 +1,47 @@
+package json
+
+import (
+	"github.com/goccy/go-json/internal/encoder"
+)
+
+type (
+	// FieldQuery you can dynamically filter the fields in the structure by creating a FieldQuery,
+	// adding it to context.Context using SetFieldQueryToContext and then passing it to MarshalContext.
+	// This is a type-safe operation, so it is faster than filtering using map[string]interface{}.
+	FieldQuery       = encoder.FieldQuery
+	FieldQueryString = encoder.FieldQueryString
+)
+
+var (
+	// FieldQueryFromContext get current FieldQuery from context.Context.
+	FieldQueryFromContext = encoder.FieldQueryFromContext
+	// SetFieldQueryToContext set current FieldQuery to context.Context.
+	SetFieldQueryToContext = encoder.SetFieldQueryToContext
+)
+
+// BuildFieldQuery builds FieldQuery by fieldName or sub field query.
+// First, specify the field name that you want to keep in structure type.
+// If the field you want to keep is a structure type, by creating a sub field query using BuildSubFieldQuery,
+// you can select the fields you want to keep in the structure.
+// This description can be written recursively.
+func BuildFieldQuery(fields ...FieldQueryString) (*FieldQuery, error) {
+	query, err := Marshal(fields)
+	if err != nil {
+		return nil, err
+	}
+	return FieldQueryString(query).Build()
+}
+
+// BuildSubFieldQuery builds sub field query.
+func BuildSubFieldQuery(name string) *SubFieldQuery {
+	return &SubFieldQuery{name: name}
+}
+
+type SubFieldQuery struct {
+	name string
+}
+
+func (q *SubFieldQuery) Fields(fields ...FieldQueryString) FieldQueryString {
+	query, _ := Marshal(map[string][]FieldQueryString{q.name: fields})
+	return FieldQueryString(query)
+}