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>

deploy/sdk/flatpay.js

@@ -0,0 +1,112 @@
+// FlatRender Pay — drop-in Node client for the ZarinPal broker (pay.flatrender.ir).
+// Zero dependencies: Node 18+ (global fetch) + built-in crypto. CommonJS.
+//
+//   const { FlatPay } = require("./flatpay");
+//   const pay = new FlatPay({ apiKey: process.env.FLATPAY_KEY, secret: process.env.FLATPAY_SECRET });
+//
+//   // 1. create + redirect
+//   const r = await pay.createPayment({ amount: 50000, currency: "IRT",
+//     description: "اشتراک", clientRef: order.id, returnUrl: "https://meezi.ir/pay/return",
+//     metadata: { userId: user.id } });
+//   res.redirect(r.payment_url);
+//
+//   // 2. on your return_url handler — confirm authoritatively
+//   const txn = await pay.inquire(req.query.id);
+//   if (txn.status === "Paid") { /* grant */ }
+//
+//   // 3. webhook (recommended) — Express:
+//   app.post("/flatpay/webhook", express.raw({ type: "*/*" }), (req, res) => {
+//     if (!pay.verifyWebhook(req.body, req.get("X-FlatPay-Signature"))) return res.sendStatus(401);
+//     const ev = JSON.parse(req.body.toString("utf8"));
+//     if (ev.status === "Paid") { /* idempotent grant keyed on ev.id / ev.client_ref */ }
+//     res.sendStatus(200);
+//   });
+
+const crypto = require("crypto");
+
+const DEFAULT_BASE = "https://pay.flatrender.ir";
+
+function hmac(secret, message) {
+  return crypto.createHmac("sha256", secret).update(message).digest("hex");
+}
+
+function timingSafeEqualHex(a, b) {
+  try {
+    const ba = Buffer.from(a, "hex");
+    const bb = Buffer.from(b, "hex");
+    return ba.length === bb.length && crypto.timingSafeEqual(ba, bb);
+  } catch {
+    return false;
+  }
+}
+
+class FlatPay {
+  constructor({ apiKey, secret, baseUrl = DEFAULT_BASE } = {}) {
+    if (!apiKey || !secret) throw new Error("FlatPay: apiKey and secret are required");
+    this.apiKey = apiKey;
+    this.secret = secret;
+    this.baseUrl = baseUrl.replace(/\/+$/, "");
+  }
+
+  async _signedPost(path, payload) {
+    const body = JSON.stringify(payload);
+    const res = await fetch(this.baseUrl + path, {
+      method: "POST",
+      headers: {
+        "Content-Type": "application/json",
+        "X-Api-Key": this.apiKey,
+        "X-Signature": hmac(this.secret, body),
+      },
+      body,
+    });
+    const data = await res.json().catch(() => ({}));
+    if (!res.ok) {
+      const err = new Error(data.message || `FlatPay ${path} failed (${res.status})`);
+      err.code = data.code;
+      err.status = res.status;
+      throw err;
+    }
+    return data;
+  }
+
+  /** Create a payment. Returns { id, status, payment_url, authority, amount_rial }. */
+  createPayment({ amount, currency = "IRR", description, clientRef, returnUrl, mobile, email, metadata }) {
+    if (!returnUrl) throw new Error("FlatPay: returnUrl is required");
+    return this._signedPost("/v1/pay/request", {
+      amount,
+      currency,
+      description,
+      client_ref: clientRef,
+      return_url: returnUrl,
+      mobile,
+      email,
+      metadata,
+    });
+  }
+
+  /** Authoritative server-side status check. Returns the full transaction. */
+  inquire(id) {
+    return this._signedPost("/v1/pay/inquiry", { id });
+  }
+
+  /**
+   * Verify the signed return-redirect query.
+   * Pass the query params { id, status, ref_id, sign } AND the amount_rial you got
+   * from createPayment/inquire (the redirect itself doesn't carry the amount).
+   */
+  verifyRedirect({ id, status, ref_id = "", sign }, amountRial) {
+    const message = `${id}.${status}.${ref_id}.${amountRial}`;
+    return !!sign && timingSafeEqualHex(hmac(this.secret, message), sign);
+  }
+
+  /**
+   * Verify a webhook. `rawBody` MUST be the exact bytes received (Buffer or string —
+   * do not re-stringify a parsed object, signatures won't match).
+   */
+  verifyWebhook(rawBody, signatureHeader) {
+    const msg = Buffer.isBuffer(rawBody) ? rawBody : Buffer.from(String(rawBody), "utf8");
+    return !!signatureHeader && timingSafeEqualHex(hmac(this.secret, msg), signatureHeader);
+  }
+}
+
+module.exports = { FlatPay, hmac };