Fix product grids with 2, 4, 5 or 6 columns dropping a column

[jasperf]

Problem

assets/css/woocommerce.css replaces the gap on woocommerce/product-template and rewrites the grid track formula to match, but only for columns-3 (the comment says it is the only variant the theme's own templates use). Every other columns-N keeps WooCommerce's formula, which assumes WooCommerce's own 20px gap. With the theme's wider gap each track comes out wider than 1/N of the row and auto-fill fits one column fewer.

Found while building store sections for Aludra: a product collection set to four columns with four products rendered 3 + 1.

Fix

Add the matching rule for columns-2, -4, -5 and -6, same shape as the existing columns-3 rule. N columns share N - 1 gaps, so each track gives up (N - 1) / N of one gap. The 150px floor is the block's own and still folds the grid to two columns on a phone. The theme's templates are all three-column and are unaffected. Version 1.18.4.

Testing

On the Aviendha demo subsite with a four-product collection at columns-4:

• Desktop: four products across (274px each); before, 3 + 1.
• Mobile (390px): two columns (157px each).
• /shop/ archive (three columns): unchanged.

CSS only; no templates or patterns changed.