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/option.go

@@ -0,0 +1,79 @@
+package json
+
+import (
+	"io"
+
+	"github.com/goccy/go-json/internal/decoder"
+	"github.com/goccy/go-json/internal/encoder"
+)
+
+type EncodeOption = encoder.Option
+type EncodeOptionFunc func(*EncodeOption)
+
+// UnorderedMap doesn't sort when encoding map type.
+func UnorderedMap() EncodeOptionFunc {
+	return func(opt *EncodeOption) {
+		opt.Flag |= encoder.UnorderedMapOption
+	}
+}
+
+// DisableHTMLEscape disables escaping of HTML characters ( '&', '<', '>' ) when encoding string.
+func DisableHTMLEscape() EncodeOptionFunc {
+	return func(opt *EncodeOption) {
+		opt.Flag &= ^encoder.HTMLEscapeOption
+	}
+}
+
+// DisableNormalizeUTF8
+// By default, when encoding string, UTF8 characters in the range of 0x80 - 0xFF are processed by applying \ufffd for invalid code and escaping for \u2028 and \u2029.
+// This option disables this behaviour. You can expect faster speeds by applying this option, but be careful.
+// encoding/json implements here: https://github.com/golang/go/blob/6178d25fc0b28724b1b5aec2b1b74fc06d9294c7/src/encoding/json/encode.go#L1067-L1093.
+func DisableNormalizeUTF8() EncodeOptionFunc {
+	return func(opt *EncodeOption) {
+		opt.Flag &= ^encoder.NormalizeUTF8Option
+	}
+}
+
+// Debug outputs debug information when panic occurs during encoding.
+func Debug() EncodeOptionFunc {
+	return func(opt *EncodeOption) {
+		opt.Flag |= encoder.DebugOption
+	}
+}
+
+// DebugWith sets the destination to write debug messages.
+func DebugWith(w io.Writer) EncodeOptionFunc {
+	return func(opt *EncodeOption) {
+		opt.DebugOut = w
+	}
+}
+
+// DebugDOT sets the destination to write opcodes graph.
+func DebugDOT(w io.WriteCloser) EncodeOptionFunc {
+	return func(opt *EncodeOption) {
+		opt.DebugDOTOut = w
+	}
+}
+
+// Colorize add an identifier for coloring to the string of the encoded result.
+func Colorize(scheme *ColorScheme) EncodeOptionFunc {
+	return func(opt *EncodeOption) {
+		opt.Flag |= encoder.ColorizeOption
+		opt.ColorScheme = scheme
+	}
+}
+
+type DecodeOption = decoder.Option
+type DecodeOptionFunc func(*DecodeOption)
+
+// DecodeFieldPriorityFirstWin
+// in the default behavior, go-json, like encoding/json,
+// will reflect the result of the last evaluation when a field with the same name exists.
+// This option allow you to change this behavior.
+// this option reflects the result of the first evaluation if a field with the same name exists.
+// This behavior has a performance advantage as it allows the subsequent strings to be skipped if all fields have been evaluated.
+func DecodeFieldPriorityFirstWin() DecodeOptionFunc {
+	return func(opt *DecodeOption) {
+		opt.Flags |= decoder.FirstWinOption
+	}
+}