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/landing/Caddyfile

@@ -18,18 +18,9 @@
 	@shell not path /assets/*
 	header @shell Cache-Control "no-cache"
 
-	# The static public offer page, rendered from ui/legal/offer_ru.md at build
-	# time into dist/offer/index.html (vite emit-offer plugin). Served with its own
-	# index so /offer/ resolves to /srv/offer/index.html rather than falling to the
-	# landing shell below (whose index is landing.html). A bare /offer redirects in.
-	handle /offer {
-		redir * /offer/ permanent
-	}
-	handle /offer/* {
-		file_server {
-			index index.html
-		}
-	}
+	# The public offer page (/offer/) is no longer served here: the contour caddy routes it to the
+	# render sidecar, which splices the live catalog price list into ui/legal/offer_ru.md. This
+	# container never sees /offer/, so it carries no offer assets (the vite emit-offer plugin is gone).
 
 	# An unknown path falls back to the landing shell (the gateway's old "/"
 	# behaviour); "/" itself resolves through the index below.