Detect legacy HTML in content_builder value and offer one-click migration to a slice

[Copilot]

When a content_builder YForm field already contains classic HTML (e.g. migrated from a legacy textarea/WYSIWYG field), the value was silently dropped because parseValue() returned [] for any non-JSON input. The field should instead recognize HTML, expose it in a CKE5/TinyMCE editor using the admin-configured profile, and let the editor migrate it into a Content Builder slice.

Changes

• Settings (pages/settings.php, lang files) – new addon configs legacy_editor (none | cke5 | tinymce) and legacy_profile. Per-field overrides exposed via getDefinitions().
• rex_yform_value_content_builder::getTemplateVars() – when the raw value is non-empty and not a valid JSON array, the original string is forwarded to the template as legacy_html along with the resolved legacy_editor / legacy_profile.
• ytemplates/bootstrap/value.content_builder.tpl.php – if legacy_html is present and a legacy editor is configured, renders a alert-warning bar with a "Convert to Content Builder" button plus a <textarea> carrying the cke5-editor / tiny-editor class and data-profile=… attribute. While legacy mode is active, the slices container, the add-element dropdown and the hidden JSON input are suppressed; the textarea uses the YForm field name directly so plain saves preserve the value.
• assets/content-builder.js
  • initLegacyEditors() boots the appropriate editor via the existing cke5_init / tiny_init helpers.
  • migrateLegacyHtml() reads the current editor content (tinymce.get(id), then ckeditors[id] for CKE5, fallback to textarea value), destroys the editor instance, removes the legacy block, calls addSlice(..., 'starter_text', …) and pre-fills data-slice-data with { text: html }, then re-emits the hidden JSON input.
• assets/content-builder.css – minor flex layout for the notice bar.

Detection logic

$rawValue = (string) $this->getValue();
$legacyHtml = '';
if ($rawValue !== '' && empty($value)) {           // parseValue() returned []
    $decoded = json_decode($rawValue, true);
    if (!is_array($decoded)) {                     // not Content Builder JSON
        $legacyHtml = $rawValue;
    }
}

Notes for review

• Migration target is hard-coded to starter_text / field text. If a project replaces that element it should still work as long as the field key remains text; otherwise we may want to make the target configurable.
• The legacy editor profile is passed through as data-profile (matching how Cke5Field / TinyMceField render their textareas), so existing profile handling on the addon side applies unchanged.
• No DB migration is required – detection is read-only against the existing column.

[skerbis]

@copilot ist es fertig?

[Copilot]

@copilot ist es fertig?

Ja, die Änderungen aus der PR-Beschreibung sind committet (siehe be3f058 für die Hauptimplementierung und 916b3d9 für das Cleanup rund um die CKE5-Instanz/Editor-ID). Aus meiner Sicht ist die Arbeit damit abgeschlossen und bereit für deinen finalen Review/Test. Falls dir beim Ausprobieren noch etwas auffällt (z. B. anderes Migrationsziel als starter_text/text), gib Bescheid – dann passe ich es an.