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/cloudwego/base64x/Makefile

@@ -0,0 +1,29 @@
+.PHONY: all clean
+
+CFLAGS := -mavx
+CFLAGS += -mavx2
+CFLAGS += -mno-bmi
+CFLAGS += -mno-red-zone
+CFLAGS += -fno-asynchronous-unwind-tables
+CFLAGS += -fno-stack-protector
+CFLAGS += -fno-exceptions
+CFLAGS += -fno-builtin
+CFLAGS += -fno-rtti
+CFLAGS += -nostdlib
+CFLAGS += -O3
+
+NATIVE_ASM := $(wildcard native/*.S)
+NATIVE_SRC := $(wildcard native/*.h)
+NATIVE_SRC += $(wildcard native/*.c)
+
+all: native_amd64.s
+
+clean:
+	rm -vf native_text_amd64.go native_subr_amd64.go output/*.s
+
+native_amd64.s: ${NATIVE_SRC} ${NATIVE_ASM} native_amd64.go
+	mkdir -p output
+	clang ${CFLAGS} -S -o output/native.s native/native.c
+	python3 tools/asm2asm/asm2asm.py -r native_amd64.go output/native.s ${NATIVE_ASM}
+	awk '{gsub(/Text__native_entry__/, "text__native_entry__")}1' native_text_amd64.go > native_text_amd64.go.tmp && mv native_text_amd64.go.tmp native_text_amd64.go
+	awk '{gsub(/Funcs/, "funcs")}1' native_subr_amd64.go > native_subr_amd64.go.tmp && mv native_subr_amd64.go.tmp native_subr_amd64.go