feat: Add SVG favicon

Replace the empty data: URI in base.html with a real SVG favicon.
Going with a broom emoji thematic to the project's purpose (cleaning
download queues). It's a single self-contained .svg file in static/,
no additional dependencies, and easy to swap later if a custom design
is preferred.

ManiMatter approved the addition in the PR thread; addresses
Dark3clipse's review point on browser-tab branding.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: lolimmlost

src/web/static/favicon.svg

@@ -4,7 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>{% block title %}Decluttarr{% endblock %}</title>
-    <link rel="icon" href="data:,">
+    <link rel="icon" type="image/svg+xml" href="{{ request.url_for('static', path='favicon.svg') }}">
     <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@picocss/pico@2/css/pico.min.css"
           integrity="sha384-L1dWfspMTHU/ApYnFiMz2QID/PlP1xCW9visvBdbEkOLkSSWsP6ZJWhPw6apiXxU" crossorigin="anonymous">
     <script>