Translate pages, areas, menus, forms and posts field by field instead of rebuilding them

A site can have further languages (Settings → Languages). A page is built once; each language
adds only its texts, keyed by the stable block IDs, plus its own address under /en/… (ADR 111,
document schema v27, migration 20261009000100 for page_translation).

- Editor: DE | EN switch, a list of all texts with original, state (missing, translated,
  original changed) and filter; structure stays with the main language. Undo, drafts,
  publishing and revisions cover all languages at once.
- Website: /en and translated slugs, lang, canonical, hreflang with x-default, og:locale,
  sitemap; links to translated pages follow the language; a language switch block.
- Header, footer and linked sections translate the same way; menu entries carry labels per
  language; fixed template texts come from a small dictionary.
- Forms: labels, help, options, button and success message per language; messages and the
  step script speak the language, the submission and the email stay in the main language.
- Posts, archives, category names, consent text and the 404 page follow the language.
- Single-language sites see none of it and never touch the new table.

The forms administration becomes an overview with one row per form and its own edit page;
fields are one line each with details collapsed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

templates/admin/menu-entry.html.twig

@@ -9,6 +9,9 @@
         <summary><strong class="menu-entry-title">{{ row.label }}</strong><span class="menu-entry-kind">{{ row.type == 'page' ? 'Seitenlink' : 'Eigener Link' }}</span><svg class="menu-chevron" viewBox="0 0 24 24" width="20" height="20" aria-hidden="true" fill="none" stroke="currentColor" stroke-width="2"><path d="m6 9 6 6 6-6"/></svg></summary>
         <div class="menu-entry-fields">
             <label for="menu-label-{{ n }}">Beschriftung</label><input id="menu-label-{{ n }}" data-key="label" name="items[{{ n }}][label]" maxlength="80" required value="{{ row.label }}">
+            {% for sprache in languages|default([]) %}
+            <label for="menu-label_{{ sprache.code }}-{{ n }}">Beschriftung {{ sprache.name }}</label><input id="menu-label_{{ sprache.code }}-{{ n }}" data-key="label_{{ sprache.code }}" name="items[{{ n }}][label_{{ sprache.code }}]" maxlength="80" lang="{{ sprache.code }}"{{ sprache.rtl ? ' dir="rtl"' : '' }} value="{{ row.labels[sprache.code]|default('') }}" placeholder="Leer: wie „{{ row.label }}“">
+            {% endfor %}
             {% if row.type == 'page' %}
                 {% include 'admin/content-picker.html.twig' with {id: 'menu-target-' ~ n, name: 'items[' ~ n ~ '][pageId]', label: 'Verknüpfter Inhalt', selected: row.page} %}
                 <label for="menu-anchor-{{ n }}">Sprungziel (optional)</label><input id="menu-anchor-{{ n }}" data-key="anchor" name="items[{{ n }}][anchor]" maxlength="65" value="{{ row.anchor }}" placeholder="kontakt">