v0.6.0

Phone drawer, light and dark themes. A minor release under 0.x, so it can break a site: see "Migrating from 0.5" in the README.

• The header collapses on phones (40rem and narrower), and wherever the links do not fit, into a square menu button on the left, the site title in the middle and a light/dark theme button on the right. The menu button opens the links in a drawer that slides in from the left. A link, the backdrop, the close button and Escape close it.
• The page follows the system colour scheme until the visitor presses the theme button. Every colour token, the rose theme included, holds a light and a dark value with light-dark(). New SiteConfig.themeColorLight sets the browser bar colour in the light theme.
• SiteHeader has a required title prop, and its markup changed (.header-bar, nav.nav-links, dialog.site-drawer).
• ProfileCard inverts its white social icons in the light theme.
• Speculation rules prefetch only pages under the site's base path.
• publish.yml fails unless the release tag matches the package.json version.