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>

README.md

@@ -186,7 +186,7 @@ GET /avr/raw?cmd=SSFUN ?            # any Telnet command, every line back
 ```bash
 python3 app.py --demo                       # fake speakers, real interface
 python3 -m unittest discover -s tests -t .  # runs against a fake HEOS network
-python3 tools/make_icons.py                 # redraw the home-screen icon
+python3 tools/make_icons.py                 # re-render the icons from static/logo.svg
 ```
 
 ## Layout