feat(icons): spectrum aperture icon set + dedicated tray variant

Regenerate the LedGrab icon family from a single Pillow script
(build/generate_icon.py): a rounded-square aperture traced by a
continuous RGB color-wheel stroke over a vignette canvas with a soft
chromatic bloom. 4x supersampled then downsampled per output for
crispness. Outputs 192/512 standard, 512 maskable (safe-area padded
for PWA round-crops), and a new 256 transparent-background tray
variant so the taskbar icon reads cleanly against light themes
instead of showing a dark tile.

icon.ico now embeds 16/24/32/48/64/128/256 frames sourced from the
transparent tray master, fixing the dark-square halo around the
file/taskbar icon on light Windows themes.

__main__ picks icon-tray.png for the tray and falls back to
icon-192.png when the tray asset isn't present (older bundles /
forks).

server/src/ledgrab/__main__.py

@@ -49,7 +49,8 @@ from ledgrab.utils.win_shutdown import WindowsShutdownGuard  # noqa: E402
 setup_logging()
 logger = get_logger(__name__)
 
-_ICON_PATH = Path(__file__).parent / "static" / "icons" / "icon-192.png"
+_ICON_PATH = Path(__file__).parent / "static" / "icons" / "icon-tray.png"
+_ICON_FALLBACK_PATH = Path(__file__).parent / "static" / "icons" / "icon-192.png"
 
 
 def _run_server(server: uvicorn.Server) -> None:
@@ -154,8 +155,9 @@ def main() -> None:
             ).start()
 
         # Tray on main thread (blocking)
+        tray_icon = _ICON_PATH if _ICON_PATH.exists() else _ICON_FALLBACK_PATH
         tray = TrayManager(
-            icon_path=_ICON_PATH,
+            icon_path=tray_icon,
             port=config.server.port,
             on_exit=lambda: _request_shutdown(server),
         )