feat(offer): live catalog price list in the public offer, served by the render sidecar

Robokassa moderation requires the public offer to list every digital good with
its price. Move /offer/ off the static landing container to the render sidecar:
it splices the live catalog price list (§4.4) into the owner-edited
ui/legal/offer_ru.md and renders it with the shared ui/src/lib/offer.ts — one
renderer, no drift, always matching the current catalog with no redeploy.

- backend: /api/v1/internal/offer/pricing (internal, off the edge allow-list)
  projects the active catalog into two markdown tables — chip packs priced per
  rail (roubles / VK votes / Telegram Stars) and chip-priced values — through
  payments.Money so no float reaches the page. Cached in memory: warmed at boot,
  marked stale on every catalog mutation, so a served render issues no query.
- renderer: GET /offer/ fetches the tables and substitutes them at the
  <#pricing_template#> marker, then renders; offer_ru.md is baked into the image
  and marked is bundled from ui. GET /offer -> 301. Only /offer/ is edge-exposed.
- caddy: route /offer/ to the sidecar; drop the now-dead landing /offer/
  handlers and the vite emit-offer plugin.
- offer: fill §4.3 (the chip-payment wording) and drop the in-page back link.
- landing footer: a feedback link (the offer's Telegram contact) beside the
  offer link.
- docs (ARCHITECTURE, FUNCTIONAL +_ru, renderer README), CI /offer/ probe,
  unit + integration + node tests.

renderer/src/server.mjs

@@ -1,20 +1,43 @@
-// The render sidecar: a minimal internal HTTP service the backend calls to rasterize the
-// finished-game export image. It runs the same drawGameImage the browser build ships
-// (bundled from ui/src/lib at image build time) on skia-canvas, with system fonts from
-// the image (Liberation Sans + Noto Color Emoji via fontconfig).
+// The render sidecar: a minimal internal HTTP service on skia-canvas and the shared ui/src/lib
+// renderers (bundled from ui/src/lib at image build time). It serves two surfaces:
 //
 //   POST /render  {game, moves, alphabet, labels, dateLocale, hostname, scale?} → image/png
+//   GET  /offer/  → text/html  (the public offer page: ui/legal/offer_ru.md with the live catalog
+//                   price list spliced in — the only edge-exposed route; caddy routes /offer/ here)
+//   GET  /offer   → 301 /offer/
 //   GET  /healthz → 200
 //
-// The service is internal-only (docker network `internal`); authentication, participant
-// checks and the signed public URL all live in the backend — this process only draws.
+// /render is internal-only (the backend calls it; authentication, participant checks and the signed
+// public URL live in the backend). /offer/ is reachable from the edge but read-only and unprivileged
+// — it fetches the price list from the backend's internal endpoint and renders the committed offer
+// markdown; no user input reaches it.
 import { createServer } from 'node:http';
+import { readFileSync } from 'node:fs';
 import { renderRequest } from './render.mjs';
+import { renderOffer } from './offer.mjs';
 
 const PORT = Number(process.env.RENDERER_PORT || 8090);
 // A render request is a finished game's journal — generously capped.
 const MAX_BODY = 2 * 1024 * 1024;
 
+// The offer prose is baked into the image (renderer/Dockerfile) and read once at boot; only the
+// price list is dynamic (fetched per request). The backend endpoint is internal (off the edge
+// allow-list) and serves the tables from its in-memory cache. RENDERER_OFFER_MD overrides the baked
+// path for a local run (point it at ../ui/legal/offer_ru.md).
+const OFFER_MD = readFileSync(process.env.RENDERER_OFFER_MD || new URL('../legal/offer_ru.md', import.meta.url), 'utf8');
+const OFFER_PRICING_URL =
+  (process.env.RENDERER_BACKEND_URL || 'http://backend:8080') + '/api/v1/internal/offer/pricing';
+
+// fetchOfferPricing returns the two catalog price tables as markdown from the backend, or throws a
+// 502 (upstream error) / 504 (timeout) so the offer never renders with a broken price list.
+async function fetchOfferPricing() {
+  const resp = await fetch(OFFER_PRICING_URL, { signal: AbortSignal.timeout(5000) });
+  if (!resp.ok) {
+    throw Object.assign(new Error(`offer pricing upstream ${resp.status}`), { status: 502 });
+  }
+  return resp.text();
+}
+
 function readBody(req) {
   return new Promise((resolve, reject) => {
     const chunks = [];
@@ -35,11 +58,23 @@ function readBody(req) {
 
 const server = createServer(async (req, res) => {
   try {
-    if (req.method === 'GET' && req.url === '/healthz') {
+    const path = (req.url || '').split('?')[0];
+    if (req.method === 'GET' && path === '/healthz') {
       res.writeHead(200, { 'content-type': 'text/plain' }).end('ok');
       return;
     }
-    if (req.method === 'POST' && req.url === '/render') {
+    if (req.method === 'GET' && path === '/offer') {
+      res.writeHead(301, { location: '/offer/' }).end();
+      return;
+    }
+    if (req.method === 'GET' && path === '/offer/') {
+      const html = renderOffer(OFFER_MD, await fetchOfferPricing());
+      res
+        .writeHead(200, { 'content-type': 'text/html; charset=utf-8', 'cache-control': 'no-cache' })
+        .end(html);
+      return;
+    }
+    if (req.method === 'POST' && path === '/render') {
       const png = await renderRequest(JSON.parse(await readBody(req)));
       res.writeHead(200, { 'content-type': 'image/png', 'content-length': png.length }).end(png);
       return;