Fix: run text format filters (media_embed) on accordion item body

MR!27 (3.1.0) fixed field_block_item not being reliably rendered by switching the template to read directly off the loaded block_content entity (block_content.field_block_item / paragraph.body.value|raw).

That bypasses Drupal's text format filter pipeline entirely: raw stored values are printed with |raw instead of being run through check_markup(), so any media embedded via the media_embed filter ( tags inserted by the CKEditor Media Library button) is never converted to an tag - it leaks into the page as literal unprocessed markup.

Build each item's title/body render array explicitly via the field API's ->view() method in the preprocess hook (PHP, not Twig - Twig's sandbox policy blocks calling ->view() from the template) so it still reads reliably off the loaded entity (keeping MR!27's fix) while running through the entity's configured field formatter/filters correctly.

Claude-Session: https://claude.ai/code/session_016SL2SK8bxJSVRSnapSkcfb