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/.golangci.yml

@@ -0,0 +1,83 @@
+run:
+  skip-files:
+    - encode_optype.go
+    - ".*_test\\.go$"
+
+linters-settings:
+  govet:
+    enable-all: true
+    disable:
+      - shadow
+
+linters:
+  enable-all: true
+  disable:
+    - dogsled
+    - dupl
+    - exhaustive
+    - exhaustivestruct
+    - errorlint
+    - forbidigo
+    - funlen
+    - gci
+    - gochecknoglobals
+    - gochecknoinits
+    - gocognit
+    - gocritic
+    - gocyclo
+    - godot
+    - godox
+    - goerr113
+    - gofumpt
+    - gomnd
+    - gosec
+    - ifshort
+    - lll
+    - makezero
+    - nakedret
+    - nestif
+    - nlreturn
+    - paralleltest
+    - testpackage
+    - thelper
+    - wrapcheck
+    - interfacer
+    - lll
+    - nakedret
+    - nestif
+    - nlreturn
+    - testpackage
+    - wsl
+    - varnamelen
+    - nilnil
+    - ireturn
+    - govet
+    - forcetypeassert
+    - cyclop
+    - containedctx
+    - revive
+
+issues:
+  exclude-rules:
+    # not needed
+    - path: /*.go
+      text: "ST1003: should not use underscores in package names"
+      linters:
+        - stylecheck
+    - path: /*.go
+      text: "don't use an underscore in package name"
+      linters:
+        - golint
+    - path: rtype.go
+      linters:
+        - golint
+        - stylecheck
+    - path: error.go
+      linters:
+        - staticcheck
+
+  # Maximum issues count per one linter. Set to 0 to disable. Default is 50.
+  max-issues-per-linter: 0
+
+  # Maximum count of issues with the same text. Set to 0 to disable. Default is 3.
+  max-same-issues: 0