Use the HEOS mark, in white, for the header and the icon

The word HEOS at the top of the panel becomes the mark itself, and the
home-screen icons are rendered from the same file so there is one place
to change it. All white on transparent: the panel is dark, and iOS lays
a transparent apple-touch-icon over black.

make_icons.py no longer draws its own glyph -- it rasterises logo.svg
with headless Chromium, which is heavier than the old arithmetic but the
only way to render real paths without a system SVG library. The PNGs are
committed, so it only has to run when the logo changes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

templates/index.html

@@ -21,7 +21,7 @@
 
 <div class="app">
   <header class="top">
-    <h1>{{ app_name }}</h1>
+    <h1><img class="logo" src="{{ url_for('static', filename='logo.svg') }}" alt="{{ app_name }}"></h1>
     <button class="icon-button" data-role="refresh" aria-label="Refresh">
       <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M20 12a8 8 0 1 1-2.34-5.66M20 4v5h-5"/></svg>
     </button>