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.

deploy/caddy/Caddyfile

@@ -107,6 +107,15 @@
 		}
 	}
 
+	# The public offer page is rendered by the render sidecar: it splices the live catalog price
+	# list (backend, internal) into the committed ui/legal/offer_ru.md and returns the HTML. Only
+	# /offer/ is exposed here — the sidecar's /render stays off this allow-list, internal-only. Kept
+	# disjoint from the landing/app paths so the catch-all below never shadows it.
+	@offer path /offer /offer/*
+	handle @offer {
+		reverse_proxy renderer:8090
+	}
+
 	# Everything else — the public landing at / and any stray path — is static.
 	handle {
 		reverse_proxy landing:80