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.

backend/cmd/backend/main.go

@@ -283,6 +283,13 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	}
 	logger.Info("payments domain ready")
 
+	// Warm the public-offer price list cache so /offer/ serves the current catalog from the first
+	// request; it is reprojected lazily thereafter on any catalog edit. Non-fatal — a transient
+	// failure here only defers the projection to the first read.
+	if _, err := paymentsSvc.OfferPricing(ctx); err != nil {
+		logger.Warn("offer pricing warm failed; will project on first request", zap.Error(err))
+	}
+
 	// Wire the payments surface into the domains that consume it: the online-game hint wallet
 	// and the account-merge wallet fold. Done after the reachability check so a broken payments
 	// schema fails boot before anything depends on it.