feat(ui): serve the public offer at /offer/ with a landing footer link

The offer is the legal document a purchase accepts, needed before real-money
intake goes live. Convert the source PDF to an editable ui/legal/offer_ru.md and
render it to a standalone static dist/offer/index.html at build (a vite
emit-offer plugin using marked); the landing container serves it at /offer/,
with a bare /offer redirecting in. Add a small centered "Публичная оферта"
footer link on the landing (ru/en) and a CI probe asserting /offer/ serves the
page rather than silently falling through to the landing shell.

ui/vite.config.ts

@@ -3,6 +3,7 @@ import { resolve } from 'node:path';
 import { defineConfig, type Plugin } from 'vite';
 import { svelte } from '@sveltejs/vite-plugin-svelte';
 import { VitePWA } from 'vite-plugin-pwa';
+import { renderOfferHtml } from './src/lib/offer';
 
 /**
  * injectBootVersion stamps the app version into index.html's boot-capability guard, replacing its
@@ -38,6 +39,22 @@ function emitPolyfills(): Plugin {
   };
 }
 
+/**
+ * emitOffer renders the public offer markdown (legal/offer_ru.md) to a standalone
+ * static page and emits it as dist/offer/index.html, which the landing container
+ * serves at /offer/ (deploy/landing/Caddyfile). The markdown is the owner-editable
+ * source of truth, so the page is regenerated from it on every build.
+ */
+function emitOffer(): Plugin {
+  return {
+    name: 'emit-offer',
+    generateBundle() {
+      const md = readFileSync(resolve(import.meta.dirname, 'legal/offer_ru.md'), 'utf8');
+      this.emitFile({ type: 'asset', fileName: 'offer/index.html', source: renderOfferHtml(md) });
+    },
+  };
+}
+
 // The edge Connect service is scrabble.edge.v1.Gateway; the gateway serves it over
 // h2c on :8081 by default. In dev we proxy the RPC path so the browser (which can
 // not speak h2c directly) talks to the dev server on the same origin. In `mock`
@@ -60,6 +77,7 @@ export default defineConfig(({ mode }) => ({
   plugins: [
     svelte(),
     emitPolyfills(),
+    emitOffer(),
     injectBootVersion(),
     // App-shell precache for the offline mode: a custom (injectManifest) service worker precaches
     // index.html + the hashed assets so the installed web PWA cold-launches with no network. It