Re-layout masonry when fields are resized

[cairocoder01]

#2898

Related to DiscipleTools/disciple-tools-web-components#198 which removes the resize observer inside dt-file-upload, since this branch puts in in the theme js

[github-actions]

Code Review

No High severity issues found.

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Summary: The change is small, correct, and well-targeted. The selector .grid .bordered-box .cell accurately matches the field-row <div class="cell"> elements nested inside each tile's .bordered-box (per single-template.php:364), and the shared resizeTimeout correctly debounces across both multiple simultaneous entries and rapid successive callbacks. The /* global ResizeObserver */ comment correctly satisfies the no-undef: 'error' ESLint rule since ResizeObserver is not in the eslint.config.mjs globals list. Ready to merge.