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.

ui/e2e/landing.spec.ts

@@ -59,13 +59,18 @@ test('the landing shows a web-version entry linking /app/, with a caption', asyn
   await expect(page.getByText('Веб-версия')).toBeVisible();
 });
 
-// The footer carries a public-offer link to the static /offer/ page (rendered from
-// ui/legal/offer_ru.md at build; the legal document a purchase accepts).
-test('the landing footer links to the public offer at /offer/', async ({ page }) => {
+// The footer carries the public-offer link (/offer/ — the legal document a purchase accepts,
+// rendered by the render sidecar) and, beside it, the feedback link to the Telegram bot the offer
+// lists as the seller's contact.
+test('the landing footer links to the public offer and the feedback bot', async ({ page }) => {
   await page.goto('/landing.html');
   await expect(page.getByText(/Играй в «Эрудита»/)).toBeVisible(); // Russian by default
 
   const offer = page.getByRole('link', { name: 'Публичная оферта' });
   await expect(offer).toBeVisible();
   expect(await offer.getAttribute('href')).toBe('/offer/');
+
+  const feedback = page.getByRole('link', { name: 'Обратная связь' });
+  await expect(feedback).toBeVisible();
+  expect(await feedback.getAttribute('href')).toBe('https://t.me/Erudit_GameBot');
 });