Fix review form overflow on phones, bump to 1.18.1

[jasperf]

Problem

On single product pages, the review form's inputs, select and textarea (assets/css/woocommerce.css) set width: 100% plus padding and a border under the default content-box sizing. The name and email fields ran 6-7px past their column, giving every product page a horizontal scrollbar at 360-414px.

Changes

• assets/css/woocommerce.css: add box-sizing: border-box to the review form field rule.
• style.css §6.7: the post comment form fields have the same width: 100% plus padding. They did not overflow, because core's comments-form block styles already apply border-box, but the theme rule now declares it itself. Hardening only, no visible change.
• Version 1.18.1 in style.css, CHANGELOG.md, readme.txt and package.json.

Testing

Synced to the local demo multisite and compared scrollWidth with the viewport in headless Chromium at 360, 414, 600, 768, 860, 900, 1024, 1186, 1280, 1366, 1440, 1512 and 1920px:

• Before: all 18 Aviendha product pages overflowed by 6-7px at 360 and 414px.
• After: no overflow on any product page, or on Home, About, Services, Contact, Shop, My Account, the sample post or the sample page.
• The post comment form fields measured border-box with their right edge flush to the column, both before and after.

Cart and checkout still overflow locally. That comes from a missing thumbnail image in the demo subsite's uploads (the files were not restored), not from theme code.