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/base.html.twig

@@ -18,7 +18,7 @@
        Importzeile sie kennen muss. Sie steht vor jedem Modul-Skript; spaeter geladen wirkt sie
        nicht mehr. #}
     <script type="importmap" nonce="{{ csp_nonce() }}">{"imports":{
-{%- for modul in ['editor-model', 'media', 'design-panel', 'button-design', 'color-control', 'rich-text', 'canvas-overlay', 'library-previews', 'preview-containers', 'page-picker', 'motion', 'slider', 'live-search', 'icons'] %}
+{%- for modul in ['editor-model', 'media', 'design-panel', 'button-design', 'color-control', 'rich-text', 'canvas-overlay', 'library-previews', 'preview-containers', 'page-picker', 'motion', 'slider', 'live-search', 'icons', 'translate'] %}
         "/assets/{{ modul }}.js": "/assets/{{ modul }}.js?v={{ kant_version() }}"{{ loop.last ? '' : ',' }}
 {%- endfor %}
     }}</script>