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>

assets/css/main.css

@@ -107,12 +107,20 @@ header.site .inner {
   flex-wrap: wrap;
 }
 header.site .brand {
+  display: flex;
+  align-items: center;
+  gap: 0.6rem;
   font-family: var(--font-heading);
   font-weight: 700;
   font-size: 1.1rem;
   color: var(--bg);
   text-decoration: none;
 }
+header.site .brand svg {
+  height: 28px;
+  width: auto;
+  display: block;
+}
 header.site nav {
   display: flex;
   gap: 1.5rem;