Stylify CSS loads before theme CSS and cannot override it

### Problem/Motivation

Stylify currently attaches saved CSS through `html_head` as inline
`

` (and similar) tags. In a typical theme, `html_head` is printed by `head-placeholder`, which appears *before* `css-placeholder`. Theme CSS such as `style.css` / `style1.css` is printed later. Because of cascade order, Stylify rules lose to equal-specificity theme rules. Example: - Stylify: `body.node-9 header#header { position: absolute; z-index: 9999; }` - Theme CSS loads after the Stylify `` tag, so the override does not apply. A second issue appears when logged in: Toolbar / BigPipe can invoke the CSS renderer more than once. Duplicate Stylify CSS can leak into page markup and show as visible text (including near the toolbar / Logout link).