Use the JARL wordmark in the header and as the README banner

The header now shows the login page's wordmark letters (without the rule)
instead of "Jarl" set in Cinzel, so the bundled Cinzel font, its preload
and its licence stanza in the .deb's copyright file are removed: the web
UI needs no web font.

The README opens with the login page's banner, the logo above the
wordmark (artwork/banner.svg). scripts/banner.py builds it from the web
UI's logo.js and brand.js, with light and dark colors, and logo.py runs
it after tracing the logo.

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

internal/web/static/index.html

@@ -5,7 +5,6 @@
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <title>Jarl</title>
 <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>