fix(i18n): keep en navigation within /en/ via pagePrefix

- build-pages.mjs: add pagePrefix (locale-root-relative, no en offset)
- use pagePrefix for nav links: logo, back-home, footer design-system/
  cookie-policy/, FAB #contact, cookie-notice link, cookie-policy body
  link, case-page #skills/#projects anchors (assetPrefix pointed to site
  root and leaked en pages to ru)
- docs/translation.md: document assetPrefix vs pagePrefix

src/partials/cookie-notice.en.html

@@ -1,7 +1,7 @@
 <aside class="cookie-notice glass-neutral" hidden data-cookie-notice>
       <p class="cookie-notice__text">
         This site uses cookies for a comfortable experience. Read more in
-        <a href="{{assetPrefix}}cookie-policy/" data-cookie-policy-link>cookie policy</a>.
+        <a href="{{pagePrefix}}cookie-policy/" data-cookie-policy-link>cookie policy</a>.
       </p>
       <button type="button" class="btn btn--secondary btn--flat cookie-notice__accept" data-cookie-accept>
         <span>Accept</span>

src/partials/cookie-notice.html

@@ -1,7 +1,7 @@
 <aside class="cookie-notice glass-neutral" hidden data-cookie-notice>
       <p class="cookie-notice__text">
         Сайт использует cookie для комфортной работы. Подробнее — в
-        <a href="{{assetPrefix}}cookie-policy/" data-cookie-policy-link>политике cookie</a>.
+        <a href="{{pagePrefix}}cookie-policy/" data-cookie-policy-link>cookie policy</a>.
       </p>
       <button type="button" class="btn btn--secondary btn--flat cookie-notice__accept" data-cookie-accept>
         <span>Принять</span>

src/partials/fab-stack-home-contact.html

@@ -55,7 +55,7 @@
           </div>
         </div>
       </div>
-      <a class="fab fab--primary" href="{{assetPrefix}}#contact" aria-label="Связаться">
+      <a class="fab fab--primary" href="{{pagePrefix}}#contact" aria-label="Связаться">
         <span class="fab-primary__ico" aria-hidden="true"></span>
       </a>
     </div>

src/partials/footer.html

@@ -2,6 +2,6 @@
       <div class="footer__inner">
         <span class="footer__chunk footer__chunk--date">© 2015–2026<span class="footer__sep" aria-hidden="true"> · </span></span>
         <span class="footer__chunk footer__chunk--main">{{i18n:footer.credit}}</span>
-        <span class="footer__chunk footer__chunk--meta footer__attr"><span class="footer__sep" aria-hidden="true"> · </span><a href="{{assetPrefix}}cases/design-system/">{{i18n:footer.designSystem}}</a><span class="footer__sep" aria-hidden="true"> · </span><a href="{{assetPrefix}}cookie-policy/">{{i18n:footer.cookiePolicy}}</a></span>
+        <span class="footer__chunk footer__chunk--meta footer__attr"><span class="footer__sep" aria-hidden="true"> · </span><a href="{{pagePrefix}}cases/design-system/">{{i18n:footer.designSystem}}</a><span class="footer__sep" aria-hidden="true"> · </span><a href="{{pagePrefix}}cookie-policy/">{{i18n:footer.cookiePolicy}}</a></span>
       </div>
     </footer>

src/partials/header-case.html

@@ -1,7 +1,7 @@
 <a class="skip-link" href="#case-main">{{i18n:skip.case}}</a>
     <header class="header" data-theme-picker>
       <div class="header__inner">
-        <a class="logo" href="{{assetPrefix}}" aria-label="{{i18n:logo.aria}}">НМ</a>
+        <a class="logo" href="{{pagePrefix}}" aria-label="{{i18n:logo.aria}}">НМ</a>
         <div class="header__cluster">
           <nav class="nav" aria-label="{{i18n:nav.aria}}">
             <a href="#contact">{{i18n:nav.contact}}</a>

src/partials/header-minimal.html

@@ -2,10 +2,10 @@
 
     <header class="header" data-theme-picker>
       <div class="header__inner">
-        <a class="logo" href="{{assetPrefix}}" aria-label="{{i18n:logo.aria}}">НМ</a>
+        <a class="logo" href="{{pagePrefix}}" aria-label="{{i18n:logo.aria}}">НМ</a>
         <div class="header__cluster">
           <nav class="nav" aria-label="{{i18n:nav.aria}}">
-            <a href="{{assetPrefix}}">{{i18n:back.home}}</a>
+            <a href="{{pagePrefix}}">{{i18n:back.home}}</a>
           </nav>
           {{> lang-switch}}
         </div>