Tighten the SVG viewBox to the actual content bounding box and
remove hardcoded width/height attributes so the browser no longer
adds horizontal padding via preserveAspectRatio. The "h" wordmark
now left-aligns with the page content below it.
Replace the error icon SVG path (which had an off-center X) with
a simple circle + two crossed lines drawn from a centered viewBox.
Both icons now use fill="currentColor" for dark mode adaptation.
Updates juanfont/headscale#3182
Move favicon.png, style.css, and headscale.svg to hscontrol/assets/
and create a single assets.go file with all embed directives.
Update hscontrol/handlers.go and hscontrol/templates/general.go to
use the centralized assets package.