feat: #2994188 Add repeatable Wikipedia content and improve image handling

Adds an optional repeatable Wikipedia content field that keeps each article, its images and editable ALT text together. Improves image selection and previews, licensing and caption controls, article URL support, non-English image lists, unavailable-content messages and per-article introduction visibility.

Existing plain-text fields, formatters and tokens remain supported. Run database updates and rebuild caches; conversion to the new field is optional and requires copying values and updating displays. Local image downloads are outside this MR.

Validation

• Pipeline #1000611 passed PHPUnit and PHPStan for the current, previous-major and next-major Drupal variants.
• Composer validation, coding standards, CSpell, ESLint and Stylelint passed.
• Local browser checks covered image/article AJAX controls. The introduction-column update preserved existing current and revision data.
• The Drupal 10 static-analysis job follows the documented compatibility workaround for newer optional attributes; runtime tests and Drupal 11/12 analysis use the original source.

AI-Generated: Yes (OpenAI Codex assisted with implementation, testing and documentation.)

Closes #2994188 (closed)