- Create public/assets/css/system.css with all 280 lines of CSS that were
inline in system.php: tab bar, status cards, PHP info grid, disk bar,
log viewer, nginx config viewer, and syntax-highlight classes.
- Disk bar dynamic values (width %, colour) moved from PHP-interpolated CSS
rules to CSS custom properties (--disk-pct, --disk-color) set on the
element via an inline style attribute; static .disk-bar rule in system.css
consumes them via var().
- system.php JS block (tab-select auto-nav + copy-to-clipboard) moved to
$extraJsInline heredoc; footer.php emits it before </body> — keeps it
out of the document <head> and removes the bare <script> after </main>.
- system.php now sets $extraCss = ['/assets/css/system.css'] so head.php
emits a proper <link> in <head>, consistent with all other admin pages.
- No behaviour change; system.php is now zero inline CSS/JS.
