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/utils.go

@@ -0,0 +1,164 @@
+// Copyright 2014 Manu Martinez-Almeida. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package gin
+
+import (
+	"encoding/xml"
+	"net/http"
+	"os"
+	"path"
+	"reflect"
+	"runtime"
+	"strings"
+	"unicode"
+)
+
+// BindKey indicates a default bind key.
+const BindKey = "_gin-gonic/gin/bindkey"
+
+// Bind is a helper function for given interface object and returns a Gin middleware.
+func Bind(val any) HandlerFunc {
+	value := reflect.ValueOf(val)
+	if value.Kind() == reflect.Ptr {
+		panic(`Bind struct can not be a pointer. Example:
+	Use: gin.Bind(Struct{}) instead of gin.Bind(&Struct{})
+`)
+	}
+	typ := value.Type()
+
+	return func(c *Context) {
+		obj := reflect.New(typ).Interface()
+		if c.Bind(obj) == nil {
+			c.Set(BindKey, obj)
+		}
+	}
+}
+
+// WrapF is a helper function for wrapping http.HandlerFunc and returns a Gin middleware.
+func WrapF(f http.HandlerFunc) HandlerFunc {
+	return func(c *Context) {
+		f(c.Writer, c.Request)
+	}
+}
+
+// WrapH is a helper function for wrapping http.Handler and returns a Gin middleware.
+func WrapH(h http.Handler) HandlerFunc {
+	return func(c *Context) {
+		h.ServeHTTP(c.Writer, c.Request)
+	}
+}
+
+// H is a shortcut for map[string]any
+type H map[string]any
+
+// MarshalXML allows type H to be used with xml.Marshal.
+func (h H) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
+	start.Name = xml.Name{
+		Space: "",
+		Local: "map",
+	}
+	if err := e.EncodeToken(start); err != nil {
+		return err
+	}
+	for key, value := range h {
+		elem := xml.StartElement{
+			Name: xml.Name{Space: "", Local: key},
+			Attr: []xml.Attr{},
+		}
+		if err := e.EncodeElement(value, elem); err != nil {
+			return err
+		}
+	}
+
+	return e.EncodeToken(xml.EndElement{Name: start.Name})
+}
+
+func assert1(guard bool, text string) {
+	if !guard {
+		panic(text)
+	}
+}
+
+func filterFlags(content string) string {
+	for i, char := range content {
+		if char == ' ' || char == ';' {
+			return content[:i]
+		}
+	}
+	return content
+}
+
+func chooseData(custom, wildcard any) any {
+	if custom != nil {
+		return custom
+	}
+	if wildcard != nil {
+		return wildcard
+	}
+	panic("negotiation config is invalid")
+}
+
+func parseAccept(acceptHeader string) []string {
+	parts := strings.Split(acceptHeader, ",")
+	out := make([]string, 0, len(parts))
+	for _, part := range parts {
+		if i := strings.IndexByte(part, ';'); i > 0 {
+			part = part[:i]
+		}
+		if part = strings.TrimSpace(part); part != "" {
+			out = append(out, part)
+		}
+	}
+	return out
+}
+
+func lastChar(str string) uint8 {
+	if str == "" {
+		panic("The length of the string can't be 0")
+	}
+	return str[len(str)-1]
+}
+
+func nameOfFunction(f any) string {
+	return runtime.FuncForPC(reflect.ValueOf(f).Pointer()).Name()
+}
+
+func joinPaths(absolutePath, relativePath string) string {
+	if relativePath == "" {
+		return absolutePath
+	}
+
+	finalPath := path.Join(absolutePath, relativePath)
+	if lastChar(relativePath) == '/' && lastChar(finalPath) != '/' {
+		return finalPath + "/"
+	}
+	return finalPath
+}
+
+func resolveAddress(addr []string) string {
+	switch len(addr) {
+	case 0:
+		if port := os.Getenv("PORT"); port != "" {
+			debugPrint("Environment variable PORT=\"%s\"", port)
+			return ":" + port
+		}
+		debugPrint("Environment variable PORT is undefined. Using port :8080 by default")
+		return ":8080"
+	case 1:
+		return addr[0]
+	default:
+		panic("too many parameters")
+	}
+}
+
+// https://stackoverflow.com/questions/53069040/checking-a-string-contains-only-ascii-characters
+func isASCII(s string) bool {
+	for i := 0; i < len(s); i++ {
+		if s[i] > unicode.MaxASCII {
+			return false
+		}
+	}
+	return true
+}