Add root-wood mark to the site header

Traced from a piece of petrified root wood the user owns, simplified into
a flat currentColor SVG so it matches the header text in both light and
dark mode, plus a bio line explaining the connection.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

layouts/_default/baseof.html

@@ -21,7 +21,11 @@
 
   <header class="site">
     <div class="inner">
-      <a class="brand" href="/">{{ .Site.Title }}</a>
+      {{ $rootMark := resources.Get "images/reground-root.svg" }}
+      <a class="brand" href="/">
+        {{ $rootMark.Content | safeHTML }}
+        <span>{{ .Site.Title }}</span>
+      </a>
       <nav aria-label="Primary">
         {{ range .Site.Menus.main }}
         <a href="{{ .URL }}">{{ .Name }}</a>