feat(site): prerender every locale and publish structured data, llms.txt and sitemaps

Crawlers received an empty client-rendered shell (107 characters of text);
most AI crawlers do not run JavaScript, so the product was invisible to them.

- Build renders each locale to static HTML (/ for Korean, /en/ … /vi/) with
  src/entry-server.tsx + scripts/prerender.mjs; the browser hydrates the same
  locale. The language menu links to those pages instead of switching in place.
- Per-locale head: title, description, canonical, hreflang (+ x-default /en/),
  Open Graph and X cards with a per-locale 1200x630 image.
- JSON-LD graph: Organization, WebSite, WebPage, SoftwareApplication (KRW
  offers, version, release date, download URL from the canonical sources),
  HowTo and FAQPage. No invented ratings.
- robots.txt (search, ai-input and ai-train allowed; /app, /api, invites
  excluded), sitemap.xml with language alternates, llms.txt and llms-full.txt
  generated from the same translations and canonical values.
- IndexNow key and a post-deploy ping (Bing, Naver, Yandex).
- A factual "at a glance" section and two FAQ answers (recognised languages,
  where data is stored) in all 10 languages.
- Icons, apple-touch-icon and web manifest; asset base is now absolute so
  sub-path pages load the same bundle.

Verified: 3.6k-7.7k characters of text per page, no hydration warnings,
no overflow at 320/1440 in six locales, axe 0, Lighthouse mobile SEO,
accessibility and best practices 100.

site/vite.config.ts

@@ -17,6 +17,12 @@ const safePublicFiles = [
   'privacy/index.html',
   'terms/index.html',
   'delete-account/index.html',
+  // 검색·공유용 자산 (scripts/render-brand-assets.mjs 가 만든다)
+  'site.webmanifest',
+  // IndexNow 소유 확인 키(공개 값). scripts/ci/ping-indexnow.mjs 가 같은 파일을 쓴다.
+  '5d886cca4138946b8488203724b2f53d.txt',
+  'icons',
+  'og',
 ]
 
 export default defineConfig({
@@ -26,16 +32,25 @@ export default defineConfig({
   publicDir: false,
   plugins: [
     react(),
-    {
-      name: 'copy-safe-public-files',
-      closeBundle() {
-        for (const relativePath of safePublicFiles) {
-          const destination = join(siteRoot, 'dist', relativePath)
-          mkdirSync(dirname(destination), { recursive: true })
-          cpSync(join(siteRoot, 'public', relativePath), destination, { errorOnExist: true })
-        }
-      },
-    },
+    (() => {
+      // 서버용 빌드(`vite build --ssr`, dist-ssr)에서는 복사하지 않는다 — 브라우저 빌드가 이미 복사했다.
+      let isSsrBuild = false
+      return {
+        name: 'copy-safe-public-files',
+        configResolved(config: { build: { ssr: unknown } }) {
+          isSsrBuild = Boolean(config.build.ssr)
+        },
+        closeBundle() {
+          if (isSsrBuild) return
+          for (const relativePath of safePublicFiles) {
+            const destination = join(siteRoot, 'dist', relativePath)
+            mkdirSync(dirname(destination), { recursive: true })
+            cpSync(join(siteRoot, 'public', relativePath), destination, { errorOnExist: true, recursive: true })
+          }
+        },
+      }
+    })(),
   ],
-  base: './',
+  // 언어별 페이지(/en/ 등)에서도 자산을 찾도록 절대 경로를 쓴다.
+  base: '/',
 })