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/src/Landing.svelte

@@ -125,7 +125,13 @@
   </section>
 
   <footer class="ft">
-    <a class="offer" href="/offer/">{t('landing.offer')}</a>
+    <span class="legal">
+      <a class="offer" href="/offer/">{t('landing.offer')}</a>
+      <span class="sep" aria-hidden="true">|</span>
+      <!-- The feedback bot: the same Telegram contact the offer lists (section 11 «Реквизиты»);
+           external, opens in a new tab. -->
+      <a class="offer" href="https://t.me/Erudit_GameBot" target="_blank" rel="noopener noreferrer">{t('landing.feedback')}</a>
+    </span>
     <span>{t('about.version', { v: __APP_VERSION__ })}</span>
   </footer>
 </main>
@@ -287,6 +293,14 @@
     color: var(--text-muted);
     font-size: 0.8rem;
   }
+  .ft .legal {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+  }
+  .ft .sep {
+    color: var(--text-muted);
+  }
   .ft .offer {
     color: inherit;
   }