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/jackc/pgservicefile/pgservicefile.go

@@ -0,0 +1,81 @@
+// Package pgservicefile is a parser for PostgreSQL service files (e.g. .pg_service.conf).
+package pgservicefile
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+type Service struct {
+	Name     string
+	Settings map[string]string
+}
+
+type Servicefile struct {
+	Services       []*Service
+	servicesByName map[string]*Service
+}
+
+// GetService returns the named service.
+func (sf *Servicefile) GetService(name string) (*Service, error) {
+	service, present := sf.servicesByName[name]
+	if !present {
+		return nil, errors.New("not found")
+	}
+	return service, nil
+}
+
+// ReadServicefile reads the file at path and parses it into a Servicefile.
+func ReadServicefile(path string) (*Servicefile, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	return ParseServicefile(f)
+}
+
+// ParseServicefile reads r and parses it into a Servicefile.
+func ParseServicefile(r io.Reader) (*Servicefile, error) {
+	servicefile := &Servicefile{}
+
+	var service *Service
+	scanner := bufio.NewScanner(r)
+	lineNum := 0
+	for scanner.Scan() {
+		lineNum += 1
+		line := scanner.Text()
+		line = strings.TrimSpace(line)
+
+		if line == "" || strings.HasPrefix(line, "#") {
+			// ignore comments and empty lines
+		} else if strings.HasPrefix(line, "[") && strings.HasSuffix(line, "]") {
+			service = &Service{Name: line[1 : len(line)-1], Settings: make(map[string]string)}
+			servicefile.Services = append(servicefile.Services, service)
+		} else if service != nil {
+			parts := strings.SplitN(line, "=", 2)
+			if len(parts) != 2 {
+				return nil, fmt.Errorf("unable to parse line %d", lineNum)
+			}
+
+			key := strings.TrimSpace(parts[0])
+			value := strings.TrimSpace(parts[1])
+
+			service.Settings[key] = value
+		} else {
+			return nil, fmt.Errorf("line %d is not in a section", lineNum)
+		}
+	}
+
+	servicefile.servicesByName = make(map[string]*Service, len(servicefile.Services))
+	for _, service := range servicefile.Services {
+		servicefile.servicesByName[service.Name] = service
+	}
+
+	return servicefile, scanner.Err()
+}