ITCR-1271: keep field media images fluid after blazy->image swap

Displays switched from the blazy formatter to core image (D11.4 config-schema fix) lose the b-lazy class, so blazy's '.b-lazy { max-width:100%; height:auto }' no longer applies and field media images overflow their container on content pages. Restore fluid sizing for .field-media-image img in the theme (Media fix for BS section). Source in src/scss/_overrides.scss; dist/css/style.css carries the compiled rule (theme build targets node <17, appended rule kept minimal). Verified on a D11.4.4 site: content image overflow (rendered 1800-1920px in a 1648px viewport) -> contained, 0 horizontal overflow.

Closes ITCR-1271