Utility sections: 404, blog, search, and more

The remaining templates are intentionally simple: 404, Article, Blog, Collections grid, Contact form, Page, Password, Search carry only the standard Color scheme and Section spacing settings. They inherit everything else — typography, colors, radii — from Theme settings, so they stay on-brand without per-template configuration.

Custom Liquid (the section form) adds a Liquid code field on top of the standard settings — the section-level counterpart of the Custom Liquid content block.