feat(ui): the key logo replaces the crown; favicon

The operator's concept, redrawn as a single-colour SVG in the accent gold:
a key whose bow is a cloverleaf holding three connected nodes, hanging on a
loop threaded through a keyring and swinging into the ring's middle, with a
small sparkle.

- static/logo/steward-logo.svg: the full mark (node graph in the bow).
- static/logo/steward-mark.svg: the small mark for 16-32 px (heavier lines,
  one centre node, two teeth); the node graph turns to mush below ~40 px.
  Used in the sidebar brand (was an inline crown) and as the favicon on every
  page and on the public share view.

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

steward/templates/dashboard/share_view.html

@@ -4,6 +4,7 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>{{ dashboard.name }} — Steward</title>
+  <link rel="icon" type="image/svg+xml" href="{{ url_for('static', filename='logo/steward-mark.svg') }}">
   <script src="{{ url_for('static', filename='vendor/htmx-2.0.4.min.js') }}"></script>
   <script src="{{ url_for('static', filename='vendor/chart-4.4.4.umd.min.js') }}"></script>
   <link rel="stylesheet" href="{{ url_for('static', filename='fonts/fonts.css') }}">