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.

docs/FUNCTIONAL.md

@@ -30,7 +30,11 @@ render with arbitrary languages, so detection would make the indexed content
 nondeterministic); a saved 🌐 choice still wins. The page carries a static Russian SEO head
 (title/description, the Open Graph card Telegram/VK link previews use, a canonical link
 pinned to the production origin, JSON-LD, the favicon set and `robots.txt`), while the SPA
-shell is `noindex` — the landing is the only indexable page.
+shell is `noindex` — the landing is the only indexable page. The footer links to the **public
+offer** (`/offer/`) and, beside it, **feedback** — the Telegram bot the offer names as the seller's
+contact. The offer page (the legal document a purchase accepts) is rendered on demand from
+`ui/legal/offer_ru.md` with its **price list** (§4.4) generated from the live product catalog, so
+the published prices always match what is currently on sale — no redeploy to update them.
 
 On the plain web the client is an **installable PWA**: a logged-out player sees an install
 call-to-action under the login form (and at the bottom of Settings) that installs the app to the