Web UI: Jarl logo and wordmark

Add the logo, a Viking jarl drawn like a woodcut whose spear-pointed crown
holds a DNS tree. It is generated by scripts/logo.py, which mirrors the
left half so the figure is exactly symmetrical, as logo.svg (white on a
Nordic-blue disc) and logo-white.svg. It links home in the header, sits on
the login page and is the favicon.

The login page shows an angular "JARL" wordmark drawn as SVG paths over a
rule with a "DNS" node, coloured from the theme. The header's "Jarl" uses
a self-hosted Cinzel Bold subset (SIL OFL); jarld serves .woff2 as
font/woff2.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/static/index.html

@@ -4,7 +4,8 @@
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <title>Jarl</title>
-<link rel="icon" href="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16'%3E%3Cpath d='M3 13 L3 6 L5.5 8.5 L8 3 L10.5 8.5 L13 6 L13 13 Z' fill='%232f5fb3'/%3E%3C/svg%3E">
+<link rel="icon" href="/assets/logo.svg" type="image/svg+xml">
+<link rel="preload" href="/assets/fonts/cinzel-bold.woff2" as="font" type="font/woff2" crossorigin>
 <link rel="stylesheet" href="/assets/style.css">
 <script type="module" src="/assets/app.js"></script>
 </head>