Table-style and flex layouts, sized like the reference browser on real sites

More real-web layout fidelity, found by testing against a wider set of sites (documentation, reference and listing pages). Older and enterprise sites often build their layouts with CSS table display, telling plain elements to behave like a table, a row or a cell, rather than newer flexbox or grid. The engine now lays these out correctly: cells sit side by side in a row instead of stacking, loose content and form fields inside such a layout are placed properly, and the whole structure matches the reference browser, so page bodies and footers built this way no longer collapse into a single column. Separately, percentage margins on a flexbox item, a common way to position a sidebar or column, are now measured against the row's width as the standard requires, so a documentation sidebar sits neatly beside the article instead of being flung across the page. These are general layout fixes that lift any site using these common techniques; others are unchanged. The overall platform score stays at 70 (correctness within layout, which was already complete).